Actually, alot of thrash is way more melodic, guitar wise, then Slipnot could ever think of being. And I like alot of music, everything from Heavy 70's stuff, to blues rock, southern rock, a bit of Jazz, Zappa, The Beatles, The Doors, progressive rock, all kinds of different forms of metal...the list goes on ..... I even like symphonic prog and symphonic metal ( Nightwish etc. ), so yeah, that's not the reason. The reason I don't like them is they sound like crap to these ears.
On top of that ,they look stupid in their little kid Halloween costumes, trying to be scary. I guess they scare some people, but for the life of me I can't figure out why Halloweenie gear scares grown people or even teenagers.
They also say some of the lamest things.."We don't wear masks, this is really us. That's a mask you have on" said to guy wearing no mask

and try to pretend their play acting at monsters is some "deep" philosophical thing. In fact it's just a ploy to get little kids to buy their stuff ie Mayor McCheese, Ronald McDonald,The Hamburgilar, Kiss ( at least they don't pretend to be"deep") ...etc.
Aside from just the way they sound, there are a lot of reasons I don't like them, but their being "melodic" isn't one of them.
That's fine though, there is plenty of stuff I like that many people hate, the difference though is I don't care what they think and don't have a need to try win them over.Or defend it. Defend my right to my own opinion sometimes sure..if I feel that is being trend upon, but I couldn't care less what people think of my taste or my bands.
"great anthemic stuff" not to these ears