Companies used to provide pensions as an incentive to stay at the company long term and not change employers, but really most of them don't care to plan for employees to stay and be developed long term.. so accordingly no pension plan is offered either.

Even ones that still offer pensions, if the support isn't there then it's in conflict with how a pension matures it's benefits. Many companies treat workers as interchangable cogs and don't provide/encourage for any exceptional wage or career growth or training. So to move upward one has to change companies - dropping (or at best pausing) the pension.

Not all companies are like this, but many (most) are. I thought this all was pretty widely understood?

So...it's not that people have to change jobs because pensions don't really exist anymore, it's that there aren't really pensions because companies don't give a shit about employees anymore?

I guess that's a reason other than pensions, technically.

Moving companies is the only way to get a promotion or a substantial raise in the current business climate. Had I stayed at the same company I'd be the highest paid developer but making 40-50% less than what a competitor has paid for my skillset.

To be clear, you're talking about direct cash, right?

Yes - this doesn't apply to big4, who realize this and tend to do a better job of stringing you along with big stock grants.