They do, and quite often IMO considering their T&C. I was at two Marriotts, Hilton Head and Richmond, back-to back, and was upgraded to suites at both. Also Honolulu Ilikai Renaissance last year. HOWEVER, per MR T&C upgrades to suites is not guaranteed. I believe the problem here is that when they were not explicitly excluded people went to the mat insisting on suite upgrades since they had a sense of entitlement; so Marriott now specifically excludes them as being guaranteed in their T&C. In so doing, they are still allowed to give suite upgrades and do. Just my opinion.

I think it varies from property to property as to whether suite upgrades are given at all. It is also determined to a certain extent with regard to the personal relationship one has with the hotel manager, and also the frequency of your stays at a particular property.. Also even those properties that do upgrade Plats to suites, they need to have a suite available for your entire stay, and who is to say the suites they do have available haven't been given out to other Platinum members. I am sorry to hear you have not received a suite upgrade. Hopefully that will change in the future,