They do have their own automobile industries, and they probably also are able to.
Why do some countries like Israel, Russia, and India use German brands as state cars?
As a comparison, China uses its own brand as a state car.
For China, it's a question of national prestige. They also don't need to be concerned about security that much (there's far less threats to Chinese head of government vs. Israel or India) - AND can afford to absorb the costs.
For others, it's the fact that their domestic car industry is either virtually non-existant (Israel), or doesn't have enough sophistication to satisfy the security requirements of head of state. And they can't afford to pay the cost to develop such production.
Notably, that was a situation with Russia's notoriously crappy automotive industry - which they deliberately decided to fix specifically for national prestige reasons, and sunk a bunch of money into producing their own domestic line (formerly known as Kortezh in 2013 and presented by Putin as Aurus in 2018, just a couple of weeks ago)