If anything, being a centralised conglomerate makes them less stable, less secure. And with less competition, they actually become more wasteful.
I.e. It’s nontrivial to be more wasteful than it would be to have multiple teams duplicating the same product.
(Strong disagree on your suggestion that the centralisation generally makes them less stable/secure, but granted on the tail risks.)
If anything, being a centralised conglomerate makes them less stable, less secure. And with less competition, they actually become more wasteful.