Nobody is saying the development hasn't slowed, but there is zero obligation for it to speed up. This project doesn't COST money, any donation is completely optional, and does not give you any miraculous shareholder-like ability to command the developer to work. Are you giving them money because you like their work? There are zero other reasons to donate aside from supporting them.
It's presumptuous to try to force someone to work on a project you likely haven't even spent a dime on. For what? Impatience? The developers can work as slowly as they want, as long as it doesn't meet the itch.io fate of never being completed due to burnout or other reasons.