WHY is this widely considered better than the original?

This was one of the first movie sequels, so it had a lot to prove. It had to make people see that a sequel could be a good thing, and as such this was a good movie.
It did exactly what a sequel should do, but also exactly what a good Frankenstein movie should do.
It expanded on the original, evolving the characters and story from the first movie to a new place through new experiences and characters, but also did, as said before, what a good 'Frankenstein' movie should do, by telling a dark story, positively dripping with gothic atmosphere, giving us moral quandries and ethical questions we can debate eternally.
Not only all that, but this movie still works as an adaptation, taking Mary Shelley's original novel (hell, Mary Shelley is even kinda in the movie) and showing us things we hadn't seen in the first film, like the scene with the blind man, which is one of the most famous parts of the book but was ignored for the first film. Now they had the time to do it in the second, and they did it great.
The whole movie works a lot like that. The first film was laying the ground-work and the second film was evolving it.
And to cap it the movie still works as just a dopey horror flick, with a scary monster causing havoc in a village, but if you want to pay attention to it you'll see the deeper messages and meanings behind all the garish makeup and fire special-effects.

The WOKE crowd enjoyed the fact that the Bride displayed feminine power by rejecting the Monsters advances.

I can see the TC's viewpoint. I like this movie but it is inferior to the original for the comedic Minnie character bringing down the tone. I was fine with the monster learning to smoke and this is coming from a non smoker. Smoking was less controversial in the mid 1930s. I can understand being disappointed the bride gets little screentime. But it is what it is.

The narrative was formed and the sheep followed. There is no rhyme or reason to it all, most people hate on sequels for no good reason and only allow a select handful to be deemed 'superior' to their originators.

Yours truly, a sequel and franchise appreciator.

It's a good movie, but I prefer "Frankenstein". However, of the three original Karloff movies, "Son of Frankenstein" is my favorite.