The reason a TB loss also needs a Giants loss to accompany it has to do with the wildcard spots.
If the Giants lose, Commanders win the division. (we are assuming that the Commanders and Panthers win their game because if they don't, we make the playoffs regardless of what happens to TB and the Giants) This would put in a three way tie for two wild card spots with Cowboys, Giants, and Bucs. Giants would own the tiebreaker (if they have the better Strength of Victory, which is a part of this scenario) then they would recieve the #5 seed. Then, we would own the tiebreaker over TB for the #6 seed. (Once again assuming we have the better strength of victory)
If Bucs were to lose but the Giants win their game, the Giants would win the NFCE, and their would be a 3 way tie for the wildcard spots with Cowboys, Commanders and Bucs. First a tiebreaker would be applied to teams from the same divisions, where we would be knocked out of contention for the #5 spot by the Commanders, and then TB would win the tiebreaker for the #5 seed. We woud be reapplied to the #6 seed, (a common misconception) where the Commander would knock us out due to head to head.
One thing to remember, its not just the Giants and Bucs losing, but also the Strength of Victory tiebreaker falling in our favor.
I hope this made some sense rather than furthur complicate things.