[wikwocket]

You nailed the reason: inventory management. It is much easier to manage rooms as equivalent fungible commodities than as special unique offerings.

Granted, there are a lot of related industries that do offer guests this privilege: theater/opera tickets, tables at fancy restaurants, luxury car rentals, etc. But these are usually luxury offerings, where they can afford to charge more (and charge premiums based on your selection) to offset the greater cost of management.