That's not true. The primary limit to carrots in this design space is the designer's own creativity. I suggested a spell that grants lots of temps. Someone else suggested that healing received by conscious characters gets a bonus, or that healing can go over your maximum. Adding any kind of benefit to healing a conscious character would be a carrot, whether that be inspiration, a damage bonus, AC bonus, or whatever.5e leaves GMs with very few avenues they can employ as a carrot. Nearly any change to problems like this one start with a need for "ok nerf this list f things like this" before you can even consider a carrot that's still below the munchkinized levels they started with in RAW & plain reading.
It's easy to be dismissive and say that the game "leaves few avenues to carrots", but before making such a claim it might be worthwhile to give some consideration as to whether or not there's any actual substance to it.