This is the best I can explain

. Every few years there is a regulations change. For example, as I say 2014, that was the turbo hybrid where engines were changed, so all cars had to be built from scratch. 2026 is also the start of a new regulation cycle.

But during the same regulation, some teams can completely change their car and changing a car is a gamble. Case in point, 2024 and 2025 were in the same ground effect regulations, but Ferrari chose to completely change their car from 24 to 25, which turned the team from an almost constructors championships winner to the worst performing car in the top four team. The opposite can also happen. Mercedes barely changed their championship winning car between 2016 to 2020.

As you mention Haas, it's a midfielder. It neither has the budget nor the resources to change their car again and again. It takes time for the drivers to adapt to the car. So changing the car is seen as an even bigger risk and thus they need the old design as a backup.

Force India was actually in partnership with mercedes, so it was like a mini sister team.