All of the big companies have armies of lawyers deeply familiar with these laws and regulations. They make their engineering teams implement processes to mitigate the issues with storage and processing.
Examples: replacing/removing external IDs, ensuring data can't be linked to users, aggregating data, not retaining data, only processing data within data centers (no data extracted to laptops), deleting old data, etc.
This is why it's slow and painful to work at big companies compared to startups. It doesn't mean that accidents don't happen, but it's pretty well thought out. The same applies to how they do qualitative research. It's got reasonably high standards which are fairly consistently applied. It's not perfect, but nothing is. There is a lot of job security and motivation for people to make it better.
Smaller companies have almost zero understanding of how to deal with this due to lack of resources and expertise. The only way they get compliant is by using good tools which force the user into a safer, more compliant posture.