I feel there are a lot of misconceptions as to why Steve Bruce is not liked amongst Newcastle fans.
As you all know, Newcastle fans hate Mike Ashley. We're one of, if not the only club in the league that deliberately aims for four out of ten every season, this has had the effect of draining hope out of the fans. Shortly before our second relegation under Ashley's watch, Rafa Benitez approached the club and was appointed manager. He was hugely popular amongst fans because he restored some optimism. Not only did he aim to build a squad that was competitive, but he engaged with fans and did a lot of charity work in the local area. Ultimately he left because he was never going to get the backing to be become a club that just about avoids relegation, year in, year out.
Enter Steve Bruce. Admittedly, whoever got the gig was going to have a rough time winning over the fanbase, but he has done absolutely nothing to do so, in fact he's done the opposite. He constantly makes back-handed digs and remarks toward fans, winding them up further. He tows the party line and takes every opportunity to kiss Ashley's backside. When his neck is on the line he also has a habit of throwing players under the bus, particularly young players. Publicly lecturing Matty Longstaff on loyalty was particularly rich, coming from one of the most disloyal men in football. He's a nice guy is Steve, or so we constantly get told by his mates in the media.
Bruce has had two season now and finished on what the face of it, are completely acceptable positions. A lot of comparisons are made to Benitez's side, but Bruce has inherited a much better side and had a lot more cash to spend. Benitez seems to get a lot of stick from opposition fans for the football he played, based on a hand full of obscenely defensive performances away to big six sides, live on Sky. The truth is toward the second half of his second PL season, we were playing some really slick, high intensity stuff (see the victories at Huddersfield away or Man City at home), but that is beside the point.
Bruce has a bit of Pardew about him, in that he keeps results ticking over, but the performances feel like the wheels are never far from coming off. This season we began with a 5-4-1. We would give the opposition 70% of the ball and try and nick a result in the last twenty minutes (providing we were still in the game). Alarm bells started to ring when we did this at Sheffield United and deservedly lost. This was in the midst of an 11 game winless run and six defeats in a row. Ashley took action and brought in Graeme Jones to oversee Bruce's day to day activities. Since Jones came in we switched to a 4-3-1-2, reliant on pressing, with the strikers splitting and running the channels. Our record has improved dramatically, to won seven, drawn five, lost five. This was also during a period when we lost players due to COVID and injury. It's became evident with this switch of style that the fitness of the players is absolutely appalling (it also raises interesting questions as to what the power dynamic is between Bruce and Jones).
The form of Willock has helped too, but how different that could have been if the club's initial move Leicester's Choudhary hasn't have fallen through. It was a much needed stroke of luck and fingers crossed we can get him on loan for another season.
A bit of a TL;DR post, but that's just a summary as to why Bruce is not liked amongst Newcastle fans. You might think some of it unreasonable, but it's not as simple as he plays unattractive football. His relationship with the fans is simply non-existent and I think he'll always struggle because of that. It's not just Newcastle fans either, you can pop over to any Aston Villa board and they will tell you a very similar story. With Ashley still running the club and Bruce in charge, it's business as usual, there is no hope or optimism of trying to improve as a football club. I'd say it's more apathy than hatred towards Bruce.