At some point I'm not sure, if "Mass Effect style" generic and unimaginative aliens comes from lack of creativity and lazy writing or more economic causes. It's generally much easier to model/animate humanoid aliens or prepare makeus/dentures, so I guess it's a mixture of both. It's worth noting that it's more forgivable for older franchises, such as Star Trek or Star Wars because technological limitations. Later it's next to impossible to drasticly redesign key visuals, but modern examples have absolutely zero excuse. ME is my favorite example how bad things can be, as it's a franchise focused on interactions with alien species which... Comes with absolutely nothing interesting, original and alien. The most interesting species of ME is straightforward Shivan rip-off.
While those factors must be a big part of it, I tend to expect there are two others that are of similar importance.
First is that a human face goes a long way to making people connect more strongly with the person behind it. Even Krogan and Turrian faces have plenty enough commonality or parallels with humanity to count for this, Salarians are a bit more of a stretch but they're still benefiting from it. I'm reminded of a writing panel who was asked 'how do you make aliens relatable?' or something to that effect, and a member of the panel who was also a cartoonist, Howard Tayler, glibly but honestly answered "I put eyebrows on them". If the story involves getting the players deeply emotionally invested in an alien, that alien having a face people can read, and to a lesser extent body language they can read, helps a ton. Obviously there's plenty of characters in media that don't have faces or whose faces you never see who people can still get attached to, but it's a big asset and I imagine very hard to pass up for games with the common ambition of imitating cinema.
Second is that Mass Effect doesn't start from a perspective of being a hard, realistic, super imaginative sci-fi. I'm not going to root around right now to see if they've talked about this in interviews any, but I'd be pretty surprised if they didn't set out to intentionally mimic those older properties that struggled with heavy limitations at least on some level. It's not "I want to make my A Mote in God's Eye
, as a video game", it's "I want to make my Star Wars/Star Trek
". At the very least, I bet that was what was in the mind of a lot of the creatives, even if someone initially wanted to be more out there. Criticizing them for not making realistically inhuman aliens is criticizing them for missing a target they weren't aiming at, to me. They wanted the dashing captain rescuing the hot space babe. Maybe that smacks of a lack of ambition, but I think that kind of iteration on the past staples is valid, inevitable, and even welcome to me, even if I wish more things existed that did other things too.