The Bucs got the Ball with 21 seconds to go at their own 20. If the Bills had guarded the sidelines instead of giving Mayfield THREE easy throws to the sideline that resulted in clock stoppages, there would have been no (nearly successful) hail mary attempt. My thinking is that if they funneled the easy completion to the middle of the field (20-25 yards downfield), a completion would have ended up running out the clock. A play of that length is going to run 6-7 seconds off the clock, and then all of the players have to race back and get set in 14 seconds before a spike. Mayfield would have been running from the 15 yard line or so.
Point is, the clock was the Bucs main enemy. Allowing them to use the sidelines with ease--with the result being four legit plays with 21 seconds and no timeouts--strikes me as pretty bad tactics.