The Niger junta that took power this summer expelled French but not US troops. From what I can tell, France had about 1,500 troops there, and the US has about 1,100 (or maybe just 600--sources differ on this).
(In October, the US Senate also voted against withdrawing US troops from Niger, 11-86.)
Have junta leaders explained why they like US troops more than the French ones?
The coup that happened in Niger in 2023 is in big part due to the security situation in the region.
To sum it up: Jihadist operation in the region pushed French army to intervene in 2013, as there are still close ties between these countries and France because of colonial history. After French intervention, the security situation got better but slowly deteriorated on the long run.
Bases were installed by the French army in the region to sustain it's operations. US bases were also installed later, but remain smaller than France's bases.
The security instability brought a series of coup in the region. Mali in 2021, Burkina Faso in 2022, Niger being the latest one in date in 2023.
It has also been documented that these coups have been helped by Wagner, the well known private military company.
The main propaganda speech these junta have been using is "France used the security situation to install military bases, with the hidden intent to bring back a soft colonial reign by exploiting our natural resources. And the security situation is not improving, thus it proves we are right". These juntas relies heavily on the anti-French sentiment and have made it the heart of their propaganda to get population's support, which is also spread by Wagner's disinformation networks.
So to answer your question, the main influential power in the region used to be France thus making it important for propaganda reasons to expel them. But otherwise it is not in their interest to expel other military forces which could be very helpful in case the security context deteriorate.
Reportedly, the junta publicly claimed that the French troops were involved in preparing to militarily restore the deposed president. (As they said nothing of the kind about the US troops, we're left to infer they claim this was mainly a French plot.)
putschists accused France of planning strikes to try to free Bazoum. They also accused France of planning a military intervention in the country, an allegation denied by France’s Foreign Minister Catherine Colonna. On Thursday, the broadcast of French media RFI and France24 was suspended in the country.
As for less stated reasons, the BBC points out that the tone of the French and US public diplomacy differed too:
after President Emmanuel Macron's vocal condemnation of the 26 July coup and his public support for Mr Bazoum, still detained in his presidential residence, Niger's new military rulers opted for a radical change of policy, demanding that the French pull out. [...]
Yet while France and the EU are cold-shouldered, with Paris blamed for problems and crises of almost any kind and even accused of supporting a 2007 rebellion by Tuareg separatists, the US retains a significant presence, sending a new ambassador to Niamey in August. [...]
Paris, and indeed Brussels, have also paid a price for their strong support for Ecowas.
The bloc's 2001 democracy and good governance protocol is the foundation for its uncompromising stance towards the coup leaders and its efforts to pressure them into taking steps towards the re-establishment of elected government, with Niger in particular targeted by a trade blockade and the threat of military intervention.
Yet Ecowas itself is widely unpopular, often portrayed as a presidents' club that has turned a blind eye to election rigging and constitutional manipulations as heads of state seek to extend their stays in power.
[...] the US has played a softer-toned public game. It waited many weeks before finally acknowledging the overthrow of Niger's elected government, which automatically, under American law, triggered the suspension of most development aid.
With a generally favourable or neutral image in West Africa, where it has no colonial history and the Cold War left no painful conflict legacy, Washington has been able to sustain diplomatic engagement with the military regimes in a way that Paris could not have done without a humiliating disavowal of its core policies and track record.
Setting an assertive tone, [Nigerien] Prime Minister Mahaman Lamine Zeine said on Wednesday: "If the Americans want to stay here with their forces they should tell us what they want to do."
Mr Zeine was not shy to hint that Niger has other suitors and alternative friends if the US does not play ball. Russia's Deputy Defence Minister Gen Yunus-Bek Evkurov visited Niamey earlier this month. [...]
However, Niger's military rulers also face awkward dilemmas. While overtures from Russia and declarations of solidarity from Burkina Faso and Mali provide a degree of political comfort, the humanitarian and security realities are grim. [...] since the coup, a combination of Ecowas trade sanctions and the suspension of much development aid, has sharply worsened living conditions for many households and jeopardised long-term development programmes.
And after many army units were redeployed to Niamey to guard against a potential Ecowas military intervention, there was a marked upsurge in jihadist attacks and inter-communal violence elsewhere in the country.
So, the US approach somewhat more resembled how they e.g. handle disagreements with Israel, i.e. tried to give the Niger junta some slack, at least in public.
