I think the primary reason was to save money
Agreed. To save money and to regain the ability to build/adjust the roster.
The 2nd apron is so confining to doing much to improve your roster that it is ridiculous.
The Celts built a title team the right way, drafting their homegrown superstar core as well as rotation players and making smart trades for talented, team-oriented guys. What do they get for their trouble ? Being penalized with roster constrictions that make it impossible to improve weak spots. I suppose that's the idea when you want a generic league of parity. The best eras in league history had a few dominant teams that were compelling to watch each season. Teams that were mis-managed paid the price with losing records.