If you look at Box and Dropbox you can see a similarity in WeTransfer's strategy. There is a "big fight" to become the centralized source where work happens. Many companies are tackling this from different angles from Invision, to Slack, to Microsoft, etc. As companies get bigger and find traction they find themselves with A LOT of capital and a large userbase to work with. We still have seen nothing yet once you have a lot of the working classes data in one place once ML is applied.

As designers its natural for us to think about always keeping things simple and having one core use, however as companies grow larger beyond that state there is a lot of money still on the table for them to capture. For VC funded/public companies this makes sense since they have to continuously grow in revenue for their shareholders no matter what. For bootstrapped founders like WeTransfer I imagine they get to a point where their money/lifestyle needs are met and they think about what more challenging things they can do to impact the world in some way.

I don't think you have to do mental gymnastics at all as their mission is to support creatives (even before this acquisition). All you have to do is spend a minute or two reading their about page, looking at their social feeds to see that the 'significant shift" you're describing isn't significant at all.

I don’t know if you’ve ever used wetransfer, if you did you’d notice that they’ve always had the creative vibe to it. This fits firmly into their strategy and image.

Then again, there are no rules that prevent companies from venturing outside of their core businesses.