That's true, to a point. But...
Last year 39 NFL QBs managed at least one game winning drive. Mac had zero. In the previous season, 33 QBs had at least one GWD, but Mac was one of 14 QBs who had only one. Mac was 16-15 in his 31 starts in that span, the Pats as a team were 18-16. It probably is true that the Pats these past 2 years did not have a lot of opportunities, but they had more than one opportunity.
Depends on how you want to define game winning drives. They had opportunites and they typically go belly up.
2021 Week 1 vs. Miami: Down 17-16, the Pats take over at midfield after a Tua INT with 8:07 left and drive to the Miami 9 when Harris fumbles.
2021 Week 4 vs Tampa Bay: Down 19-17, Pats get the ball at their own 25 with 1:52 left. Drive to the Tampa 37, Folk misses a 54-yarder in the rain. Big play on the drive was a DPI on Tampa for 20 yards.
2021 Week 5 vs. Houston: Tied 22-22, Pats get the ball with 7:17 left at their own 13. They drive to the Houston 3 and kick the game winning field goal with 11 seconds left. Big plays were a 24 yard completion to Meyers, a Bolden 25 yard run and an RTP penalty on a 3rd and 18. Once they got into field goal range they ran to kill the clock.
2021 Week 6 vs Dallas: Down 26-21 with 2:20 left, one big play to Bourne for the TD. Also converts the 2 pointer.
2021 Week 6 vs Dallas: Tied 29-29 in OT, Pats get the ball first and drive 21 yards before punting on 4th and 3 from their own 46.
2022 Week 3 vs. Baltimore: Down 31-26, Pats take over with 12:00 left after a Ravens fumble, Mac throws pick in the end zone. Gets a 2nd chance with 6:30 left and hit a big play to Agholor who fumbles.
2022 Week 12 vs NY Jets: Tied 3-3, Pats took over with 3:00 left and punted after 1 first down.
2022 Week 13 vs Minnesota: Not a game winning situation but were down 33-26 with 4:12 left. Moved it from the NE 13 to MN 30 before a sack put them in a 4th and 16 and turnover on downs.
2022 Week 14 vs. Las Vegas: Down 17-16 with 5:10 left they score in 3 plays (short run, 39 yard pass to Meyers, 34 yard TD run by Stevenson). Convert the 2 pointer.
2022 Week 15 vs. Cincy: Down 22-18 take over on the Cincy 43 following a fumble and go 7 plays (5 runs) down to the 8, Stevenson fumble.
Main takeaway from looking at it is that they have a hard time sustaining drives and have had 3 of them end on fumbles in situations where they may have won otherwise. It's also been pretty boom or bust, they either hit a big play or fizzle out. In some of these situations it's hard to tell if they don't trust Mac or if they're too hell bent on burning as much clock as possible. The Miami one in his debut is understandable. The Cincy one last year they were just keeping the ball on the ground.