If you're ten years at the same company, it's exceptional that you couldn't get an offer for significantly more money. Paying "market rate" is a policy for new hires, not existing devs as much.

And as you pointed out, that's a huge mistake. To this day I cannot understand why people simply don't do meetings where somebody says "okay guys and girls, we have a new need in the company; you 5 here aren't heavily loaded -- or we can relieve one of you of their current duties to work on the new thing -- is somebody up for it?"

I have witnessed such an approach I think twice for 17 years of career. And it worked really well the both times. Re-negotiating salaries is a matter of understanding and realizing that you now bring more value and/or carry more responsibility. For some reason HRs and CEOs absolutely hate raising wages of existing employees. They might hire somebody new at 3x the salary of a current senior engineer (seen that as well, and the new hire had significantly less expertise!) but they will be damned before they allow that current engineer get a higher wage.

It might be that they are afraid that if they raise one wage then everybody will demand the same. But I don't see how this would be different with a new hire. No more than 2 months in they will be sharing details of their arrangement with the other colleagues during the lunch break. Same thing, cat get outs of the bag sooner or later.

That phenomena -- huge resistance to raising wages of existing employees -- remains a mystery to me to this day.