So this may seem like a weird question, but bear with me.
Loads and loads of anime are based on manga, and it's a fact that has become well-known in the anime community. However, the mecha genre seems to be a tad different.
I've seen a decent amount of mecha anime in the past. However, one trend that sticks out to me is that a lot of mecha anime are original works, and not based on manga, or light novels.
Here are some examples that I was able to gather by going through the mecha genres on MyAnimeList:
- Gundam franchise- is technically a multimedia franchise, but started as a TV anime
- Code Geass - another huge mecha franchise
- Macross franchise - huge and old mecha franchise
- Neon Genesis Evangelion
- Tengen Toppa Gurren Lagann
- Darling in the FranXX
- Eureka Seven
- Suisei no Gargantia
- Kakumeiki Valvrave
- Cross Ange
- Hoshi no Koe
- Isekai no Seikishi Monogatari
- Tenkuu no Escaflowne
- Star Driver
- Aquarion series
- Heroic Age - this one's kinda iffy since the giant beings they transform into are organic (kinda like Attack on Titan), but MAL categorizes it as mecha
All of these are original anime, or started as original anime. However, when you look through other genres on MAL, there aren't a lot other genres with this many original works.
So why do mecha anime tend to be original works, more so than other genres? Why aren't there as many mecha manga or light novels?