It's directly and amply covered in the T&Cs. https://www.marriott.com/loyalty/terms/default.mi#elite

'2.1.f Non-Qualifying Rates. A “Non-Qualifying Rate” is a rate a Member pays for a Stay in a guest room at a Participating Property which does not qualify to earn Points or Miles, as well as membership tier benefits. Non-Qualifying Rates are those booked using the following methods:

i. The guest room was booked through a tour operator, online travel channel or other third-party channel including, without limitation, expedia.com, hotwire.com, priceline.com, orbitz.com, booking.com, travelocity.com; '

4.1.c. Benefits of Elite membership apply to stays on Qualifying Rates (as described in Section 2.1.e.) and are reserved for Members only and apply solely to the one guest room in which the Elite Member stays.