Lufthansa doesn't have a controlling stake in Brussels Airlines, so while there is some co-operation I think to blame Lufthansa group is misplaced.
Also, I am fairly certain the decision to delay the flight for 5 hours wasn't taken lightly, because as warakorn has pointed out the cost is paying hotels, meals and compensation for all passengers (regardless of the reason being technical problem or crew rest issues).
The valid point here, is that typically in my opinion EU airlines call-centre staff are not empowered to help with rebooking in these scenarios (as they seem to be still bound by the fare rules), whereas US airlines call-centre staff seem to have much more flexibility. The reduction and outsourcing of airline ticketing staff is happening everywhere, just in my opinion it is more successful where the call-centre staff can offer alternatives to passengers by phone.