Either way, it's poisoning the well. It's a shame that many (most?) SaaS applications lack data portability. I get that part of it is it's easier to have a custom schema than adhere to an established file format (or creating a new open format). The cynic in me believes a lot of it is good old-fashioned lock-in or casual indifference to their customers' data.
That's may even be fine for some bits of data. But, for anything I want access to long-term, I just can't trust SaaS start-ups anymore. Very few acquisitions end up with a favorable outcome for the customers. Sometimes the service gets unceremoniously shut down. In other cases the app gets folded in to some other product the parent company owns. In yet others the product suffers as the parent company tries to squeeze what it can from the existing consumer base.
I have no real interest in trying to scrape my data out of a vault so I can recreate it elsewhere. Increasingly, I limit my choices to established players with a history of long-term product support (e.g., Apple or Microsoft, but not Google) or OSS. I'm sure in the short-term I'm missing out on new functionality that could increase my productivity, but I don't like the anxiety of knowing I could lose all my data in an instant and so I don't truly engage with such products. My primary concern is no longer than the company will go out of business but rather that they'll try to shoehorn a growth model that doesn't make sense for the core product so they can then sell and sail off into the sunset.
Obsidian is an interesting case where's it's not an established company and it's not OSS, but they've made it possible for you to ensure long-term access to your data. If needed, there could be an OSS-equivalent of Obsidian to read those files. But, I'm happy to just pay them for a good product. If they were to have a big exit, that's great for them and I don't think I'd be impacted very much.
The trend in software has been a move to walled gardens and there's been strong adoption there, so I don't think my mindset on the topic is a prevailing opinion. But, I have noticed family members and such have grown increasingly tired of service shutdowns from acquisitions. Expensive devices become bricks. Important data goes away. Etc.