Why do leading ASICs manufacturers sell their chips? I understand that some people have access to cheaper electricity than others. However why not just open mining facilities in the parts of the world offering the lowest cost structure? If that is not possible, then a joint miner with those miners would seem more profitable than selling the most profitable newly invented ASICs chips to the general public.

In some situations I know people will buy older ASICs miners that are no longer profitable for various reasons including a desire to help the network or speculating on future bitcoin price increases retroactively making the mining profitable. That is not my area of focus. I am more interested in why the newest most profitable ASICs chips are being sold.
I think the simple answer is that a company doesn't have to be a "Bitcoin believer" in order to manufacture Bitcoin mining hardware.  The companies that produce ASIC chips also produce other products for other industries.  They are perfectly profitable just selling their chips to mining equipment manufactures, and probably don't feel the need to enter the world of speculation on a young, digital currency.

At their core, these companies are silicon chip factories, and there is lots of demand for custom silicon chips in the market.  There's no need for them to change up their business model and become Bitcoin mining facilities.

Don't forget that during the California Gold Rush, the wealthiest man in town was the guy selling shovels :)