Could you clarify what you mean by "LGTM?" Just people saying, "looks good to me" and doing crappy reviews, or is there some LGTM "thing" out there that everybody will use? Or something else?
There is a meme out there in the wild (or at least, I think there is a meme) that many reviewers would simply approve PRs blindly leaving a LGTM (looks good to me) comment when their internal monologue is closer to "...I have no idea what's going on here and I'm too afraid to ask at this point". I suppose it could also be sheer laziness of not wanting to parse many lines of new code, especially if you're in a situation where you don't have a 100% tight understanding of the codebase (as I have been in many a times).