Because even if they don't use those permissions today, it is easier to ask for them up front rather than reduce their update rate when rolling out stuff that does use it.

This is often combined with release notes like FB and Pinterest where they say something like "we're adding great stuff all the time but we won't tell you what it is until you've installed and can't roll back even if you hate it, so upgrade now to get the latest!"

The trend seems to be most prominent among ad supported apps, which doesn't surprise me. They need to future proof their data collection options. Can't say I blame them from a business standpoint as much as I dislike it as an end user.