Why do you think this, when the manufacturer has told you specifically that it doesn't?
No we don't. The manufacturer's page that you linked says it isn't.
Again, why would you think this, as opposed to wishing it?
Who knows? First, find and catch your EGA monitor, then suck it and see.
Because that was what the market was like at the time. Or at least Power R thought it was. You'll note that they're no longer in business.
Not everything that seems obvious to us looking back was obvious at the time. Even then, businesses and people can cling stubbornly to their own standards, while the rest of the industry standardises elsewhere. Look at Apple themselves, for example.
is a completely different adapter from the one you have in your hand.
only connect a VGA card that can run in EGA emulation mode to an EGA monitor. They don't do any conversion themselves. They're just cables.
Sorry, wishing just isn't going to make it so. Ye canna change the laws o' physics, cap'n. They call these old beasts fixed frequency monitors for a reason.
That said, if you dig up an EGA monitor, give it a go. Don't forget though, you have two sync rates to consider, not just one.