The only way you could use Sonar in the past was to pay for it.
That money paid to develop the software to where it is today. You could have used Audacity, or Reaper and never paid for the license. But, you saw value in Sonar and in return, were willing to pay for that value. Because you were, the software was able to endure to the point where another company could buy it and keep it going. So far so good.
Meanwhile, you get to keep all the current goodies - L-Phrase processors, Rapture Session, Blue Tubes plug-ins, Melodyne Essential, Addictive Drums, TTS-1, etc. as well as goodies from the past (my Pantheon reverb still works...) AND all the content that was released since X3. This represents considerable value that the people getting the "free" version today won't have.
I would hope that Cakewalk goes back to the original idea behind lifetime updates - deriving income not from the core program, but from add-ons
that people can choose to purchase or not as opposed to being rolled into the cost of an upgrade. Remember, people who already had Battery and Melodyne paid for those again when they bought X3 or Platinum. The add-ons offer people more choices.
If it makes you feel any better, new users buying the add-ons
you already have means that they're paying to help continue developing the program for
your benefit.