What are you basing this on? Warrants require probable cause (in the US at least). Are you saying that that the probable cause requirement still allows warrants to be granted very easily? Or that the probable cause requirement is not being followed?
Well, both.
Warrants may be granted very easily via the FISA courts [0]. They are unenforced in the warrantless wiretap programs [1]. If your wiretap happened to be illegal, and you want to work around this to win the court case anyway, you use parallel construction to build a case that does not rely on the secret wiretap [2]:
> Because the SOD's work is classified, DEA cases that began as NSA leads can't be seen to have originated from a NSA source.
> So what does the DEA do? It makes up the story of how the agency really came to the case in a process known as "parallel construction."
[0]: https://en.wikipedia.org/wiki/United_States_Foreign_Intellig...
[1]: https://en.wikipedia.org/wiki/NSA_warrantless_surveillance_(...
[2]: https://www.washingtonpost.com/news/the-switch/wp/2013/08/05...
[0]: https://www.reuters.com/article/us-dea-sod/exclusive-u-s-dir...
[1]: https://theintercept.com/2018/01/09/dark-side-fbi-dea-illega...
[2]: https://www.hrw.org/report/2018/01/09/dark-side/secret-origi...
Yes. Probable cause is not a significant burden and can be met with "evidence" that would normally never be admitted. Cops regularly rely on unnamed out-of-court CIs. For telephone call records, the simple fact that a phone number appeared during an investigation is likely enough for a warrant to see which other numbers it has connected to.
That said, warrants are not always needed. The logic goes that the phone company already knows who you have called. They needed that information when they connected the calls. They store that information for billing purposes. So connection/metadata isn't private because you have already shared it with the phone company. In many countries that is sufficient to moot the entire warrant debate. (This logic then extends to other data used to make connections and route internet traffic such as IP addresses.) And if the phone company/ISP is a state-owned/backed/licensed enterprise there is little privacy left to argue over.