> Startups failed because they cound not untangle own code after 4 months.

That's rare, though. If they could not untangle their own code after 4 months, it's because they were not making enough money to pay a team to untangle it - that's not a code problem, it's a revenue problem.

IOW, the startup failed because their revenue was too low.

There are orders of magnitude that failed because they did not solve the right customer problem. Code quality is merely incidental the vast majority of the time.