I could see maybe trending topics as possibly a feature that would be nice to have at launch but the others?

The following are my thoughts if I were a PM choosing features.

search - What are you going to search for when the app is brand new? I believe we did have user search as I recall using it so you must be referring to content search.

DMs - Do we know what their anticipated user projections were going to be? I could see this feature being a worthless endeavor vs other things they could have done if the userbase ended up being small.

a web version - These guys are a mobile first company, the large % of users are on mobile, their existing web properties are either in maintenance mode(facebook) or just thin wrappers(instagram). I can see why this wasn't a priority.

non-Instagram account creation - Sounds like either this was a way to bypass overhead in their typical new user generation or they felt one click signup from IG would encourage more active users/reduce issues of bots which may not have been thought out at launch. It would be interesting to learn more about this unclear part of the infra.

Europe - Even for big company launches they typically american first, likely for the same reasons why we dont see big new tech companies ever launched from Europe anymore: too many little issues dealing with all the different countries in the union, issues with complying with various regulations.