You are assuming way too much good faith. For every one that does it in earnest there's probably 10 grifters just taking advantage of the situation for their own personal benefit:
The real reason seems to me like virtue-signalling. They don't care whether they're personally offended, as that would require burning social "points" by rocking the boat but potentially getting no outcome out of it (nobody else might agree). It's "safer" to just suck it up than sacrifice social points especially when you're on the lowest ranks.
They also don't know nor care whether the protected class they are worried about is actually going to be offended. Again, rocking the boat and burning social capital for little personal benefit.
This leaves the argument of earning social capital by virtue signaling among like-minded peers. Pick a common issue you already know is popular within your target "market" (racism, sexism, "diversity & inclusion", etc) and raise the problem. This doesn't risk any social capital, after all, people like you won't disagree (for the same reasons) and people that might be on the fence or would like to add nuance wouldn't want to risk their social capital in fear of being labelled a racist/etc. It also transcends the ranks - if anything, a higher-ranking person in the company would risk much more by speaking out than someone on your rank or lower.
This eventually results in a positive feedback loop where everything will become offensive given enough time and those who disagree either comply or get pushed out. That's how you get bullshit like GitHub's "main" branch which helps nobody while continuing to sell services to ICE which you could argue actually hurts minorities.
And therein lies the problem. A subset of people get a benefit from engaging in this behavior. So of course they do it at every opportunity.
You get what you incentivize.
Until the outcome is so frequently a net negative (however slight) in so many cases that the behavior is marginalized to a negligibly small number of people/settings the behavior will persist in enough volume to be worth caring about.
The problem is that a large part of the tech industry nowadays relies on "engagement" aka monetizing user attention for the benefit of advertisers, thus extremely vulnerable to public opinion (the advertisers themselves would engage in this behavior, thus companies that supply them must also conform to it). The entire industry is on thin ice already so it makes sense for everyone to play it safe even though it just reinforces the feedback loop even more.
This is why this behavior is rarely seen in other industries that make the bulk of their money on a tangible output, both because the output is less fungible/replaceable as well as those industries' employees typically having less time to waste engaging in bullshit.
I'm just going by conversations I've had with people in person and online, and assuming that this is broadly reflective of society overall. Don't get me wrong, I am quite sure that there are people who are cancelling people for sadistic pleasure and get a kick out of torturing someone and use hot-button issues to do so. However I cannot imagine this type of person outnumbering those with good-faith concerns at a 10:1 ratio.
Other times, you get the "well it's so very easy to make this small change, it's practically rude (or suspicious) not to" - a completely wrong sentiment for many reasons, but easy to make you look difficult for arguing about.
That said, it's interesting this has come up during a discussion about how the intent behind what someone said is often either misunderstood or discarded.