Maybe, as some people say, 4 small bottles equate the same amount of plastic as one big.
But if I have a series of 1 night stays (which happens) then after each night all 4 small bottles are discarded, despite me not using but a small portion of the content of them. The big bottles would barely show signs of my consumption. So after 5 single nights the miniature bottles would have equated enough plastic to 5 big bottles, yet the big bottles in those rooms are still fine for many guests to come. Leave aside the fact that on long term stays, housekeeping will often replace the small bottles before they are empty.
The environmental benefit is obvious. If Marriott benefits as well, so be it. I can live with an initiative having more than one benefit. I can even live with Marriott doing this purely for the money, and the environmental impact just being a positive side effect.