I think it is genetic. I do not grow milts but I've noticed this in other orchids. In general, I believe many orchids needed to evolve to this. By sequentially offering blooms they will have more exposure to their pollinators therefore more likely to survive. Ive observed this in 2 ways. Some inflorescence will sequentially bloom. Others may have PB's that mature at different times. I have a very large BC Maikai that has been in bloom for months as new bulbs mature at different times. Usually smaller plants can't do that.

Due to the very large number of species and a much larger number of hybrids there must be a lot of exceptions. Including 1 of your 2 milts.

The behavior of orchids frequently gives us pleasure and amusement. That is collateral. Generally what they do is programed in their genes to procreate. So when my brassavola nodosa provides a sweet and spicy aroma at night it does please me but the effort from the plant is to attract its nocturnal pollinators.

Then there are hybrids. And the possibilities geometrically increase...

Stable conditions that are consistent throughout the growing area would help...but that would be quite the impressive setup involving big money. Even so, they still have to be the same species to flower synchronously, Longwood gardens manages to do this annually as an event of sorts.
If you are messing with a variety of orchids, and they are all in the same environment, it depends...so many variables at play, at least improbable, but not impossible (i think?). Different triggers for different orchids.
As shavedmonkey said, endemic species can evolve in very intricate ways to compensate for the lack of range they can live in.

Even though i get very ecstatic when many orchids are in bloom at the same time, that also means once they are finished the growing space will be without flowers for a while. Not that it is a bad thing, but i'm assuming to those growing orchids for flowering aesthetics, might not be too happy during that period between flowering.

I like the idea of the plant creating a sequence one way or another. As impressive as a lot blooming can be, I like the idea of a plant that stays in bloom for a while.

I can see your point, but think a lot (for me) depends on the size of the flowers relative to the rest of the plant. Sometimes a small number of blooms just gets overwhelmed by the foliage.