Failure to protect a trademark can cause the trademark to become genericized. I’m pretty sure that doesn’t apply to everything. Velcro fights hard for people to call their product “hook and loop fasteners” because they don’t want other companies to sell their products as Velcro, and it’s also why Nintendo was fighting for people to stop calling other consoles Nintendos in the 80’s and 90’s.

I don’t think you can genericize Mega Man, for example. Nobody’s going to call other types of games Mega Mans. In this case, it’s a copyright infringement, whether sanctioned or not. They’re not going to lose their trademark over Mega Man for this.