The simplest answer is that because most healers couldn't keep up with the healing requirement of earlier Raids so SE greatly reduced the healing cap so that more healers would have access to raiding.
Healers DPSing in raids has always been a thing and has always trickled down to casual content in the form of Dungeon Speed Runs. (or at the mentality of Main Heals, Support Heals + DPS)
Because SE lowered the required healing so much in Creator Savage both healers have a ton of opportunity to DPS and this has trickled down into casual content that it is pretty much expected that healers have time to help with DPS not to mention the lowered accuracy required for dungeons re-enforces this idea.