You are guessing wrong. This is one of the most basic rules of the game: no elite benefits unless you book directly with the hotel, or via a corporate rate your employer negotiated directly. Your company travel agent is doing something differently, which is to your detriment. The reason for this is simple: Marriott and all other hotel chains have to pay a percentage of what they get to the OTA, so even if the OTA rates are the same as the hotel charges, the hotel gets less money for the booking. Hence. they incentivize booking directly so they don't have to pay the fee to the OTA. This is as it is with every other hotel chain as well.

I'm amazed you've never known this, which is why everyone suspects you are a troll. The first time you booked a Marriott via Expedia or any other OTA you would have seen the same thing. Are you saying in all these 2500 nights you never tried booking with an OTA before and found out this rule?

One nice thing about Hyatt is at least for publicly available rates the rates directly available at Hyatt are always cheaper or equal to the OTA rates, so there's no incentive to book OTA unless you want the loyalty benefits of the OTA (and are willing to give up the loyalty benefits of your hotel chain). Personally I am not willing to give those up, so I always book Hyatt directly myself. If my company books it I would instruct them to use Hyatt directly as well, thankfully they'd listen to me because we are a small startup and I'm an exec.