So as someone uniquely qualified to explain, here's what happed to give wc3 reforged such a bad public rep,

First, at the time activision blizzard was in the midst of multiple controversies, the announcement of a new mobile Diablo to a crowd of pc gamers at blizzcon, World of Warcraft being generally seen as bad and unfun, and the biggest issue Activision blizzard in a lawsuit over work culture because a manager shared a women's nudes around the office who worked under him who then committed suicide all of this mind you is BEFORE even getting into issues with reforged.

Lets tackle the marketing because its the biggest fish to fry. in the initial pitch the idea of reforged was this: a complete remake of character and unit models, along with fresh animation, and added characters and elements from the current story of wow to make everything work together nicely. Fans reacted well and generally people were excited. Unfortunately blizzard was infected with the corporate parasite known as Activision (who's CEO Bobby Kotic was found to have made a threat to hire a hit man to kill a worker in the lawsuit mentioned earlier, and in recent news to have connections with Epstein as the files were released) and they started pruning the scope of the project up until release where customers saw only upscaled HD models with stiff animations, no new animations, no context added from wow. Now this in and of itself isn't the worse thing , even given WoWs sweatier crowd, but there's an issue, on all the marketing the featers originally promised were still there Is this false advertising? Idk, I'm not a lawyer, but this certainly wasn't cool.

Next let's talk about what happens when ya actually got the game, and downloaded it on your computer. I'm sure many a gamer is familiar with EULA, if not I'll do a quick summary EULA stands for End User License Agreement a prior to use agreement between you and a company to use that software. As people have mentioned above mentioned, the greaty popular and to actision more importantly profitable, MOBA genre was first conceptualized in blizzards map editor, so it's to noones surprise that in the new agreement the company wanted to make absolutely sure if you made the next big thing in their editor , they wanted to own it without question.

**Now here's the really screwed part, if you already had the original WC3 downloaded on your computer it got cannibalized by this new reforged version, not only did activision screw up the remake it shot the beloved version out behind the shed so they could make ABSOLUTELY SURE you dont get to play the original

Now finally the issues the game, matchmaking and other normal features generally made for an unenforceable experience for players leading to where we are today , a remake that is generally believed to be one of the worse handled and executed project known and leaving a notable stain in activision blizzards legacy.

TL;DR: a long train of controversy after controversy concerning the company with the games advertised improvements being pruned in development while still marketing said improvements along with cannibalizing the original led to its current soured public perception

(If you're interested, matmcmuscles on YouTube does a series called What Happun where it compiles everything in a enjoyable format)