No one made fun of Lars in the 80's.
If Metallica had only made 4 or 5 albums, then dropped of the face of the Earth, Lars would be highly regarded for all he accomplished on those legendary albums. His playing was pushing limits (at least in music people tended to listen to), and full of creative parts and some highly technical playing, particularly on And Justice for All.
When I was 18, there was hardly anyone who played like Lars. He was considered a top drummer of the era.
But then the 90's happened. And then the early 2000's. And as mentioned, Lars stopped practicing, and he was pretty open about how he didn't practice and didn't keep up. And not only did his playing stop improving, but live footage from the early 2000's shows his playing got worse. He could barely perform his own songs. And his attitude in the press didn't help.
So there were a lot of fans who used to worship the guy, or at least respect him, or who lost their respect for him.
I mean, who can respect a guy who says he doesn't practice, doesn't like to practice, and it shows in the live show? Not to mention, he stated simplifying his own parts in some of the older material.
Meanwhile, tons of drummers who grew up on Lars learned everything he did, and improved upon it, and then improved upon it some more.
And now you have so many drummers who weren't around when Lars was a thing in the 80's, who only became aware of him in the 2000's, who wonder, why the heck was this guy getting accolades for when the stuff on youtube isn't all that compared to "insert so-and-so" who is playing at a higher level.
.
Seeing Metallica live in 88/89 was completely mind-blowing. It was beyond epic.
But I get it, if you weren't there, and only have seen the post-mid 90's Lars, then he seems like a bad joke.