As someone who has actually seen the movie, I can totally see why audiences wouldn't be into it. Obviously, humor is subjective, but I feel like the raunchiness of the film went a bit too extreme, and that's not something everyone can get into.
And at least for me, a lot of the jokes fell pretty flat, and my audience kinda felt the same. Some jokes really landed, while others didn't really get any big response. I get why critics would like it, especially when it comes to the film's heartfelt moments and the whole gender-swapped teen sex comedy concept, but for people looking to laugh, I can see some people not all that enthused by it.
Then there's the R rating alienating the teens who might be interested in it, Quiet Place breaking out and grabbing some teens along the way, and Infinity War basically sucking up all of the movie buzz a la TFA back in 2015, and I can see why Blockers didn't get a big audience.