The GBU-57 needs to be dropped over the target like a traditional bomb. It can only correct trajectory, not glide.
I've read that B-2s have been dropping them on underground structures in Jemen as a warning to Iran, but sources are limited.
The B-2 bombers operating out of Diego Garcia have been reportedly using 30,000 lb GBU-57 Massive Ordnance Penetrators against underground Houthi targets.
theaviationist.com
JASSM-ER nor any other air-launched missile has the penetrating capability or the payload to destroy facilities dug in mountains. Only the GBU-57 does.