The problem is that the ISPs have demonstrated that they can block it if they want to. Some don't allow P2P apps, most block outgoing email. Legally that makes it a choice to not block file sharing, which then forces them to defend that choice. The old "Linux ISOs" argument probably isn't going to help them there.
Blocking email is easy - you just block outgoing port 25 connections to anywhere but your own server. You can block some P2P apps by blocking ports as well, but most P2P apps aren't so easy - they often run on random ports.
In the past, where the past was 15 years ago, you could - they made traffic shaping boxes that could deep packet inspect for bittorrent and such and deprioritize such traffic. Which is why most bittorrent traffic is now encrypted by default. And those companies making those boxes aren't making them anymore.
Basically unless they work on a specific port, it's extremely difficult to filter traffic these days. Data flow rates are just too high even for an NGFW (next generation firewall - basically a box that does more than basic packet filtering and stateful inspection but goes up the stack even to layer 7, and often using MITM techniques to inspect encrypted traffic).
ISP filtering these days isn't really an option short of installing filter boxes at every customer because that's about their limits on speed when you have customer internet connection speeds of over 1 gigabit being common. Even top end NGFWs, the ones costing tens to hundreds of thousands of dollars are only good for up to 100G, and ones good for 2.5/5Gbit are in the thousands of dollars range.
At the data flow rates a consumer ISP is seeing, the hardware routing systems are limited to packet headers - you aren't going to deep inspect packets. You're stuck with what layer 4 can provide, and it isn't much beyond the UDP/TCP headers at those flow rates.
About the only thing an ISP can do is implement IPv6, because IPv6 lets you go back to an individual machine. An IPv4 address only gets you a household or coarser - it's not sufficient legally to charge anyone with anything.
But if you can get down an individual PC - you can then find who's the actual person using that PC and then get back to suing teenagers again.
Maybe that's the intent - force ISPs to implement IPv6 so we go from a household and reasonable doubt of who committed the crime, to an individual user so Sony and the RIAA can go back to suing people again.
All the more to want to have NATv6 back again so you can put many people behind one IPv6 address again.
Technology goes both ways, after all. IPv4 has issues, and NAT has issues, but legallly it also hides the originator of traffic. IPv6 doesn't have that limit and now you can identify who's responsible for the traffic.