I'm very confused, if the bed bugs are in/on the mattress, and you enclose the mattress in a cover, how do the bed bugs get out of the cover?
Also wash everything you own in hot and dry on hot. Or put it in an airtight box for at least a year. They can and will live anywhere within a few feet of where you spend a lot of your time. Couches, beds, chairs, carpets, etc.
This person is downplaying how hard it can be to get rid of them.
I know of no hotels that bother with diatomaceous earth, so I presume it either doesn’t work sufficiently often, or it takes too long to work.
A quick search tells me hotels usually do heat treatment. It requires a professional (or in house set up). I suspect they also wrap the mattresses by default, but I'm not sure that's strictly a bed bug measure.
Bed bugs are everywhere though. They will infest any public space with furniture, or any space like hotels where anybody can come in and out. They have infested my local movie theaters (at least the older ones). I bet there are a lot of airlines with this issue.
The GP's post implies some sort of causal relationship between placing the cover on the mattress and the bugs then being forced to crawl over the DE. I still do not see what the relationship is.