- the New Zealand Air Force has all Western planes.
- New Zealand launches space rockets with the help of USA.
Why don't neutral countries like New Zealand purchase any strategic equipment from Russia?
New Zealand is not a neutral country. After WWII it saw the United States as its best chance of protection, and hence supported the US during the 50s and 60s. During the 1970s it became disenchanted with US foreign policy and has declared itself a nuclear free zone, but has always been part of the West.
More widely, the term "neutral country" has a narrow and specific legal meaning. It says nothing about politics. In practice most neutral countries lean in some direction, often to the point of bumping up against the legal restrictions of neutrality.
World War II provides some historical examples. Both Spain and Ireland were officially neutral. Ireland favoured the Allies in non-military ways, for instance by providing meteorological observations, while Spain favoured the Axis, even sending "volunteer" troops to fight against the Soviet Union (but not against Western Europe). The allies also exploited this against the Germans in the case of the Man who Never Was; a body carrying faked secrets was arranged to wash ashore in Spain as the allies knew that the Spanish would provide a copy of the "secrets" to the Germans.
On your specific points:
Military aircraft: a military aircraft is part of a wider system; it has communications and IFF systems that must interact with systems on the ground, and it carries ordnance which interfaces with the aircraft (e.g. smart bombs, guided missiles). Even ammunition has to be compatible with the weapon firing it. So its rather like Nikon vs Canon cameras: once you buy into a system the only way to switch is to basically junk everything you currently own and buy new from scratch. New Zealand has historically bought weapons from the West, and has no particular reason to switch.
Your rocket launch example doesn't support any claim of bias. A private US company launches small satellites from New Zealand. This seems to be a purely commercial venture of no strategic significance.
One specific area of cooperation you do not mention: New Zealand is part of the "Five Eyes" intelligence alliance.
Why don’t neutral countries like New Zealand purchase any strategic equipment from Russia.
Faulty premise contained in the question. To expand on the previous answer, far from neutral America’s “five eye” allies of which New Zealand is one, represent America’s 4 closest allies. They are the only countries America shares real time raw signals intelligence and satellite data with. Which are some of the countries closest held secrets. The reason raw signals intelligence and satellite data is so closely held is because with access to the raw data it's possible to discern the capabilities of the collection platform, as well as the signals intelligence techniques which would allow a malicious actor to compromise or mislead primary intelligence gathering avenues. The raw data would show the blind spots, the capabilities and point to counter measures.
Beyond this all of the five eye security partners hold security guarantees among each other.
The roots of the five eyes alliance was the special relationship between the US and UK forged by FDR and Churchill before and during WWII. The five eyes alliance remains between the US, UK and some former commonwealth countries.