Always look at the incentives. The Boston Bombing intelligence "failure" is not a failure of intelligence. We got exactly what the incentives were set up to deliver. The system works, it's just not spec'd out to deliver what people think it is.
A mostly law abiding protest group that dares loudly complain about the government "doing it wrong" is an actual threat to law enforcement because it is a threat to the status quo. The voters might listen to them. The voters might install politicians who make promises of "doing it right" which usually includes allocating resources on things other than law enforcement. Drug treatment instead of drug crime task forces for example. That's a real risk to law enforcement agencies and gets treated as such.
On the other hand you have two dudes with some bombs. Worst case they kill a couple hundred people and make the public hate them in the process. Sure that makes you look like incompetent fools but the public already thinks of you that way so you don't lose anything. No politician is going to get elected on a promise of turning your organization upside down because you failed to catch some lone wolves. Maybe you can even find a way to blame someone/something else and get some extra power out of it. Those guys were not a real risk to the organizations tasked with stopping people like them and were likewise ignored.
That said, as much as it pains me to defend the MA state police the failure mode of the status quo they have settled into is pretty benign. The false positive rate on terrorism is so high and they are so eager to LARP as combat troops that if they did thoroughly follow up on every tip they got they'd likely have a much higher body count than the real terrorists. Doing unethical things to maximize their incomes and minimize their work (the gripe most people have with the MA state police) is pretty harmless by comparison.
I'm not arguing that we should get rid of encryption, (nor am I saying it's even possible to defeat encryption at scale, so it was probably a bad example to go with when call detail records would have been better, but I should really be working right now), rather, I'm saying we should let law enforcement keep up with the level of technology, but we should have strong auditing processes and don't allow for situations like the FISA/FISC situation where proceedings are nearly always literally one-sided (only prosecution, defense is necessarily excluded from the proceeding) [0].
New powers will be required to deal with new situations. The SARS-CoV-2 virus, for example, has killed more Chicagoans in the past 2 months than homicide has in the past 3 years, and that is also ravaging the economy as people are correctly afraid of going out in public. Currently most people are isolating because we don't have a more precise way of separating the infected from the uninfected, but China's digital contact tracing QR-code scheme provides a much more precise separator (and per an episode of This American Life [1] that I just listened to, it actually made at least the interviewee more comfortable being in public because they knew infected or risky people were separated out). If legislators implemented very tight controls over who could use the data (and how) and there was (sufficiently) transparent and rigorous auditing, we could save lives, jobs, and businesses. I know the public won't go for it because the public justifiably doesn't trust the government to prevent abuse of this system, but I would love to live in a world where we could develop and deploy technical solutions to major problems and be confident that the technical solution would not be abused.
[0] https://scholarlycommons.law.wlu.edu/wlulr/vol72/iss3/4/