I've seen a few startups that seemed to overengineer things (or build custom solutions rather than use something off the shelf) in expectation of massive growth.
I also thought it might have been due to resume driven development and the need to keep engineers engaged so they didn't leave.
I've also seen successful startups with a monolithic rails or PHP application that ran on heroku with next to zero custom architecture components.
I've seen a few startups that seemed to overengineer things (or build custom solutions rather than use something off the shelf) in expectation of massive growth.
I also thought it might have been due to resume driven development and the need to keep engineers engaged so they didn't leave.
I've also seen successful startups with a monolithic rails or PHP application that ran on heroku with next to zero custom architecture components.