Also having to deal with the differences between different markets, internationalisation, auditing required at larger size, greater reliability requirements, et

Also having to deal with the differences between different markets, internationalisation, auditing required at larger size, greater reliability requirements, etc. And over time, the first designs will turn out to have problems, so you have to rewrite/replace/refactor, which may end up having multiple systems running in parallel for a long time. Complexity accretes.