The nice thing about stupid criminals is that they tend to be indiscriminately stupid. The ones who don't use encrypted messaging are the same ones who proceed to brag about their crimes in front of strangers, and have their phones turned on and with them during the commission of their crimes, and post incriminating pictures on Facebook, and choose equally stupid and unreliable criminal partners.
They are the low-hanging fruit, so you don't need powerful and invasive tools to catch them because they're practically self-incarcerating. When there are 100 other ways to catch them, there's no point in paying a high price just to have 101.
It's the non-stupid criminals that they have trouble catching, but those are the ones this won't catch either. So you're still paying a high price for really nothing in return.