I understand that they have to make money but it is a major inconvenience because it is a very popular game but cant they swap out some games for Forza horizon I know they’re not going to but I’m just hoping in the future that they change this.
Welcome to the community. 
Economically it actually makes sense to make the most popular games non-free. WeMod is a business, not a charity.
Horizon is no longer actively developed as Xbox 360’s popularity these days is low and declining daily. There are dozens of ways you can earn income to pay for a Diamond subscription.