I know it sounds trite, but it really isn't. It is about visibility.
The old saying "It's not what you know, it's who you know" may ring true, but a truer phrase, "It isn't just who you know, but who knows you."
On a quiet day, I get pinged with opportunities three or more times, many I quietly ignore or politely decline, others I'll let them run their natural course.
On a busy day, it is like swatting flies.
And whilst there are opportunities available, not all are worth pursuing because the price isn't right, or the problem isn't interesting, or, even though someone reached out to me, they then expect me to jump through their hoops and I've always been a lousy hoop jumper.
To make OP feel better, not all these invites are useful. I have had loads of people saying "you look great, we'd love to have you work for us!", then when you reply they're like "send a resume", then get ghosted.
I might send a C.V. if we can get past some basic questions, e.g. compensation range, remote/on-site, type of work, whether this is yet another CRUD that is no more than a pretty UI on an SQL db, and so forth.
But generally I take the attitude "I've already got a job, and you asked me, convince me I should." I'm polite and professional (most of the time) but I'm not wasting my time on leads that will go nowhere.
If I'm the ugly duckling with twenty bucks in my pocket and I espy a hot lady at the bar, sashaying up to her and saying "you should buy me a drink" ain't gonna cut it.† Too many companies are the ugly duckling.
† Though... uh... now that I think about it that actually worked with my wife so maybe you shouldn't listen to my advice.
I added "gatekeeping" for bite, but I realise there is no bad intention behind it.
Not criticising the behaviour either. It's just the state of things.