"if possible" might be the issue at hand though. None of us are privy to the ins and outs of the Senators exact financial situations, but it's pretty easy to deduce that cash flow is a real issue for this team. Wouldn't be a case of "not wanting to" as much as Melnyk not having the up front cash to shell out ~$20+ million in a calendar year.
On an unrelated note, I'm actually starting to wonder how many "allies" the Senators would have when it comes to this signing bonus stuff. There aren't very many teams left that don't hand them out. I understand it's the cost of doing business, but it would be tough for the Panthers (for example) to lobby the NHL to close that loophole after giving Bobrovsky ~half his contract in SB's. It's entirely possible I'm overthinking this angle though.
I think the signing bonus issue will be a major point in the next contract discussions with the players by many teams even some of those that have had to resort to using it to retain or obtain players. Burying bad contracts in the minor leagues is also contra-competition and I suspect will be addressed too.