But how have I formed this perspective, about a social trend? It's my own extrapolation based on... anecdotes and social media, I guess. So it's hard to know if that picture (the before, after, or how things may have changed) is accurate.
You should look for tutorials on Wireshark or better yet get a Pi-hole and block ads over your entire network while you get trustworthy stats on where your traffic is going. That's probably the easier and more useful option. Casual packet inspection used to be much easier. Common traffic like HTTP, DNS, or SMTP are increasingly encrypted, but it used to be that you'd see everything pass over the wire plainly. A lot of the data companies send home is encrypted too so you might be able to identify which apps or programs are generating the most traffic or sending it to same shady destinations, but don't expect to see what data they are collecting from watching the network.
I remember uninstalling software and dismissing it as spyware for just phoning home. The very idea of a program regularly pinging some remote host to indicate the your machine was turned on and connected to the internet was offensive. Now basically every program does this, usually excused as checking for updates.
I think a lot of the problem was as it got easier for people to get online more and more people were using the internet who didn't understand the technology or how it could be used against them. They didn't care about anything but checking sports scores and online shopping and it let companies get away with taking advantage of them in ways the old nerds would never have accepted and once those nerds were vastly outnumbered by people who didn't know or care about privacy abuses the nerds no longer mattered.