ever heard of “not invented here”? even if you have valuable IP big tech companies think they can do better even if they cannot, or are simply greedy and will spend a multiple of what your IP costs just so they don’t need to acquire you. that is what i’ve noticed. there is little logic or reason.

Keep in mind that "big companies" consist of many "small people".

If you offer them the IP for sale any decision-maker in the company that could approve paying for it will need to ask themselves: "How much would this help my career in this company personally? Or does it put me in risk of possible failure? Does it put me in competition with our other departments? How much would we need to invest our own time and efforts to integrate this IP into our product-line?".

great insight, thanks. so what is a smart way to go about this?

Become enough of a threat that they acquire-hire you or buy you to shut you down.