More underappreciated aspect is variety. US tends to be very copy-paste - once you solve someone's problem well, it's quite likely your solution is universally applicable to large swaths of the market. EU varies not only country-to-country, but often even between departments of the same company in the same building. It's not just technology, even markets for beer or coffee are likely more varied in your average EU country than in the entire US

We provide documents and services for startups and this is spot on. Once you've got past the idea of "getting investors to invest in a funding round in exchange for equity" and the obvious differences of i18n and l10n, there are real differences - in France you need to have a lawyer to be able to operate at all, and in Germany investors participate through holding companies instead of directly. And it gets more complicated when you start talking about options or convertible notes.

The complexity of getting our platform to work with all of this is as big a consideration as market size is when we're looking to expand abroad.