As far as my knowledge goes, this is a hardware limitation, but I’m not very confident on that, I could be wrong. Hardware is not an area I’m very experienced in.
Having said that, please keep in mind this is not the same for individual games, only for the Itch app itself. So even if you purchased the bundle, individual games could still offer multiple executables for multiple architectures, which you can download from the Itch website.
Because the Itch app is open-source, it’s always possible to compile it for ARM architecture, but individual games come already compiled, in which case you have to hope the developer has the game in a format that it can run on raspberry pi.