I think the WordPress project should do more to push people to move to more modern version of PHP (eg a "talk to your host nag" at the very least), but that's an issue for WordPress core not BuddyPress. The BuddyPress team should be given credit for taking this move before WordPress core. There is a line they need to walk, but they could have played it safe and stuck with 5.2 support and they chose not to. A small step perhaps, but an important one.