https://en.wikipedia.org/wiki/Data_portability

Why should I care that my data is portable? Well, it has to do with capitalism. Profit is too large of a motivator. Companies want to keep you so they can continue to profit, so they have an incentive to make it hard for you to leave, including making it hard for you to easily transfer your data to another product. A company's public relations department will strive to navigate the fine line between short term profit and long term reputation.

So for example, Google has Google Takeout, but there's a missing piece in the puzzle. There's no easy import to anywhere else. or even back to Gooogle. Email for example, is not straightforward to import to anywhere else (although there's a different way that's easier than the takeout method, but it's not mentioned).

“- When you export your mail from Gmail, each message's labels are preserved in a special X-Gmail-Labels header in your download file. While no mail client recognizes this header now, most mail clients allow for extensions to be written that could make use of the labels.
- Google does not support a direct import of .mbox files so you may need to use a 3rd party tool to open .mbox format export into Thunderbird or Apple mail.
- Gmail does support a pop3 email transfer from other email accounts into your Gmail account.”
source

More examples of headaches with different Google products: 123456

Additionally, services tend to disappear. Google has been introducing or acquiring services, and then killing them. This is a normal trend for online services backed by for profit corporations. Check out the following sites:
The Google Cemetery: https://gcemetery.co
Killed By Google: https://killedbygoogle.com

You want your data to be in a form that can be easily transferred if the service should be discontinued. If you use free-and-open-source-software (FOSS), there is almost a guarantee that the data will be standards compliant. Genuine FOSS does not have profit as a conflict of interest.

Platform coop recommends using https://midata.coop for your medical records: “ MiData, a Swiss “health data cooperative,” has created a data-exchange which will securely host member-users’ medical records. By integrating this traditional health data with emerging data streams from FitBit devices and personal genomic services, MiData aims to out-compete private, for-profit data brokers and ultimately return the control and monetization of personal data to those who generate it. ”