MM can also put conditions on their sell orders like "all or none". Maybe they do that. They show up as large quantity sell orders but few can buy, or at least delays the buy action long enough for them to cancel.
Onco yes I don’t really understand why certain commentary is offered. As to your speculation, entirely possible but with algo trading how could an fair system allow delay? Maybe that question answers itself. In any event there certainly are many here who know in detail how the MM and and order allocation/fulfillment systems work.