He was born with a silver spoon, used that to purchase great companies, and fund important research, and then assumed that the success of the projects he invested in meant that he had good business acumen, instead of recognizing that all he did was "provide money for projects which had well-known solutions (or paths to them) but lacked funding."
Then, he used that narcissistic self-aggrandizement to consider himself as "intelligent" and began opining on things, publicly, which proved that he had no comprehension of the things on which he opined. When challenged about that reality, he routinely retreated into mocking, memeing, and general non-engagement with criticism.
To that end, he misunderstands free speech (both the humanitarian necessity, and the constitutional protection in the US), economics (beyond smithian / libertarian circle jerks), labor (thinks it's "people that work for me" rather than an engagement with business partners), and various other highly-abstract, low-provability topics, which leave him at the disadvantage of having to use interpretations of statistical trends, rather than empirical, peer-challenged hard science (like physics for rockets/mining/light sensing/etc).
So, overall, you have a rich narcissist that pretends to be intelligent while employing the instincts and tactics of infantile dissidents, all the while being bad at the business side of running a business, and only ever PROVING that he can be competent at "providing money" (which he has done quite excellently, I think anyone would agree. From PayPal to Tesla to SpaceX; Elon's funding choices have been both profitable and valuable).
In that, there's not much for an engineer to appreciate about the man. Not much for a "techie" to admire. There's plenty of surface level self-congratulatory wank for anyone to aspire to (without giving it real consideration). But not a ton of true, appreciable motives, actions, or considerations. Engineers tend to revere those that do incredibly hard, laborious, tedious, or otherwise complicated work for the love of the work being done. That sounds about as far from Elon Musk as I could describe.
Which, to be clear, I think translates into "distaste", "malaise", "annoyance" or a myriad of other types of negativity that barely rise to the mantle of "inconvenience", much less "hate". But if you give an engineer an inch of real-estate to talk about what's stuck in their craw, you can be prepared to get a mile of answer. So there's a lot of "negativity" for Musk because he's an annoying person and we all commiserate about that to whatever degree we're feeling institutional, that day. Some days, he's a union-busting, selfish douche-bag who managed to launch a rocket. Other days, he's the gutless dickhead who tried to reneg on military communications for a besieged country. And on other days, still, he's just "the guy who bought twitter."
tl;dr: people are negative about him because he does so much which is collectively recognized as "shitty", and people respond to shittiness with negativity; often in commensurate amounts.