No worries cfwake
Not everyone wants to go straight to airline flying. Generally people who go modular already have a PPL so it makes no sense to go through 'foundation' stages again. Already having flying experience and possibly a few years worth of recreational flying means less money on hours building and then it's about £30k for the advanced flying stages and MCC. Of course not everyone is like that, but I think it's fair to say that a vast majority already have PPLs when starting at a modular school.
If all you want to do is fly airliners then no doubt places like OAA are better than the self improver route and if the price of an integrated course was similar to a modular course almost everyone who wants to fly airliners quickly would go integrated. However, with time and experience there's no reason why self improvers can't get to airlines. Believe it or not some even get lucky and a CV sent to an airline pays off - though when we talk about training we always talk about likelihoods, and the likelihood is that you won't get lucky. But then again you make your own luck.
What 757drivergla says is true, the big FTOs provide a trusted brand to airlines. Much like when we go to the supermarket we can trust Heinz to offer a solid, trusty sauce/soup.