As a member at the Platinum Elite tier (or above), you do get lounge access (if there's a lounge) at Sheratons -- but you also get to choose a Welcome Gift, which could be daily breakfast in the hotel restaurant for yourself and a second guest sharing the same room.

It's always possible that a particular hotel will violate the terms & conditions -- either intentionally (to cut costs) or because hotel management hasn't bothered to understand the elite benefits for their brand.

If enough Platinum Elite (and above) guests insist on the USD$100 guest compensation as documented in the terms & conditions -- very costly to the hotel -- then the hotel will get the message. That's why the Marriott Bonvoy terms & conditions provide guest compensation when hotels fail to provide guaranteed benefits.

Because the breakfast rules are so complicated, there are probably many elite members who don't know what they should expect, so they just accept what the front desk tells them.