That's probably because you've only been a professional developer for 10 years. Here's a quick history lesson:
If we go back, say, 25 years, when the term Open Source entered common usage, it was a way of describing the things that had thusfar been labeled "free software", but as a way of deemphasizing the notion of the Free Software movement that saw non-free-software as immoral. It was a term to describe things that met the Free Software Definition, but without harping on morality.
It was very much a counter-culture (it was, after all, the Free Software movement and the Open Source movement), and very much not a generic term for having access to the source. That was already super common in enterprise agreements, and nobody considered that to be open source.
Then around the early 2000s, Linux became hot shit, and some large companies wanted to avail themselves to the rising tide and began labeling their watered down versions of "source available" things as open source in an attempt to jump on the bandwagon. But that was an intentional attempt to water down the definition everyone already understood for marketing reasons.
You not knowing this history means that to some extent the marketing worked. But just realize that in arguing here, you're participating in the astroturfing. Also, get off my lawn!
I'm also often an advocate of what you're saying there, "language changes..."
But this I think is one of those cases where there is a difference, because it's also descriptive of a community, and it matters how that community sees itself. With whatever definition of open source you have, the most high traction stuff that we all rely on (I originally wrote, "most", but I think e.g. the Linux kernel matters more than a random abandoned repo on Github) is produced by people that use that older definition of open source, and mostly by people who identify with that social movement. (I for a long time was one of those people.) In this case I do believe that in that all of us now rely on open source software, that redefining it in opposition to the group of people who produce that thing is less than respectful.
Anecdotally, I've also been a professional dev for over 10 years, and have been involved with open source projects longer than that. And in my experience, "open source" almost always means you are free to modify and redistribute from the source (possibly with a requirement that you also release the code for your changes, in the case of the GPL). The exceptions are mostly companies that want to claim they are open source for marketing, without actually following the spirit of open source.
Anegdotally I have been a professional dev for 10 years and this is the first time I hear your definition of open source.