Very good point, with 8 HoL bosses it would not be to difficult to have a new one each day, but I guess they don't want us to have 10k~ food per day which eventually leads to a more steady supply of items and that leads to them not selling the purple/orange boxes in their events that they try so hard to force on us.
With regards to Osiris being mia, I can only speculate. But I think she is being stealthbuffed/nerfed or otherwise it is because when she was released she appeared like 3 times in 1 week. So maybe they are now compensating for that. But that is also specualtion because there is zero communication as to what and why it is happening.