Forza Horizon 6 lets you display cars inside player garages, but the game does not give every garage the same number of display slots by default. To show more cars, you need to buy houses with the Additional Garage Slot perk and place more Display Car Locators in that specific garage.
The short answer is that display slots are connected to player houses, not your entire car collection. Buying more houses gives you more garages to customize, while certain houses increase how many cars you can display at that location.
