A few years ago, someone made a faithful recreation of metroid 2 with 16-bits graphic... nintendo forced the author to delete it... i think the main issue is copyrighted characters.
That was definitely the reason. The same scenario has occurred quite a few times over the years, involving many different companies. I love a really good fan recreation, such as AirWalk Studio's 'Fix-it Felix Jr.' for example. However, the unpleasant fact remains that, even if they don't use the original code or assets, they're still infringing on trademarked characters and as a result are very much illegal. I've always seen the linking the Game&Watch recreations as being a big liability for RetroArch, but I suppose the gamble is that Nintendo won't bother to protect infringements related to the LCD titles.
One particular project that I hated to see shut down was an HD fan recreation of 'Mortal Kombat Trilogy' for MUGEN. Especially since Midway's own HD remake of the first three games was scrapped as well. It's off topic, but worth sharing Midway's leaked photos, as they're pretty impressive. They had actually completed filming most, if not all of the characters before pulling the plug.
It'd be a lot of work for very few ROMs. There's only a handful of examples that are truly public domain or otherwise allowed to be distributed freely. As far as open source game ports go, the RetroPie-Setup already acts as somewhat of a "store", allowing you to easily download and install precompiled binaries through a GUI without having to use anything other than your RetroPie setup.