One of the reasons the carriers want to do this is content caching. When you visit YouTube, Netflix and many other high-data usage websites these carriers have servers in their datacenter provided by these large companies to cache often accessed content.
In the case of Netflix they provide very beefy caching servers that can save petabytes of data from needing to be downloaded from outside of the carriers network. This saves the ISP money due to them having to pay other carriers for peering.
The problem with virtual private networks is the data you're accessing is encrypted and thus cannot be cached at all by the carrier. They are concerned that they've sized their networks with these caches as part of the design. If hundreds of thousands to millions of users suddenly have all their traffic uncacheable it may lead to bandwidth depletion, high latency and congestion.
You all I'm sure saw Netflix's Squid Game. A show that had all episodes released at the same time and was watched by more than 150 million people around the world. Many of those people watching it in 1080p or 4K. Almost all of those people watched it from a local ISP cache. That's how Netflix has their architecture designed, ship servers to ISP's datacenters so only a single copy of Squid Game (for instance) needs to be sent while hundreds of thousands of customers of that ISP can watch it without causing congestion for everybody.
I've laid out the problem. But I do not stand with the ISP's on this one. I feel that user privacy trumps the efficiency of their networks and companies should adapt. Netflix for instance can still do geographic based routing and use their content delivery network in specific regions to deliver content instead of at the ISP level as can Google when people watch YouTube.
There are solutions, they just cost money and are different to the current methods. I feel users shouldn't have to sacrifice privacy so some multi-billion dollar ISP's can get their way. They make enough money as it is, deal with the problem like grown ups instead of trying to abuse the court system to choose what kind of traffic you carry.