More money up front would help initially, but that's all they'll ever get from those users. Typically, users buying a license with a maintenance subscription (free upgrades for x time) is better for the business long-term if they continue development and people keep coming back.
There's a reason most software companies are doing annual subscriptions. That model doesn't really fit software like BTT imo, but the 2 years of upgrades does. Frankly I think they should double the Standard license cost and increase the lifetime license cost significantly - or even retire the offering.
Go to a Mac sub on Reddit and buy a few Standard licenses for people. Make sure to mention you don't work for BTT.