It can be very frustrating when cards from supplemental products are not on mtgo ESPECIALLY for legacy/vintage. If those cards somehow do make it MTGO its usually as very few slots in chests. If these cards are strong and in very limited supply then they are often VERY expensive. When chests contents are updated so slowly its hard to imagine how long it will take for the entirety of CLB, 40K, or the legal UNF cards to eventually come to MTGO. There are still a lot of cards from older commander sets that are not even on MTGO. It is just frustrating waiting for cards from products that I would be willing to buy slowly make it on MTGO through chests.
On the other hand, from the developer prospective I understand how difficult a task like this must be. Scryfall shows that there are roughly 1500 cards legal in eternal formats that are not currently on mtgo. It seems almost impossible to decide which cards to chose to spend the time coding and getting all the interactions to work (especially on a client that is 20 years old). How do you decide which cards, when often times people ask for cards that very niche or wont see enough play to justify spending the time making that card work.
While I think most players would prefer to have all the cards on MTGO thanks for even putting the cards on MTGO in the first place