Redis Labs was a long time sponsor for the full-time development of Redis then later compensated the creator of Redis for their rights to Redis Technology and branding who was ended up retiring from technology to write Sci-Fi books. By contrast AWS takes most of the profits whilst contributing relatively nothing back, making them the biggest leacher and the primary motivation for the relicensing to prevent mega corps with unfettered access to their future contributions that AWS repackages to compete against them.
So whilst their previous license allowed AWS to leech off them, it's now been relicensed to prevent them from profiting off their future investments without compensating anything back.
During an all-hands around 2008 I asked AWS leadership whether AWS was going to open source their technologies the answer was we're thinking about it. 16 years later it has not happened, nor it will given the record ;(
You buy the trademark/name from the original author. I'm the case of GPL or other assigned work licenses, you sell the baseline copyright and they can change it.
So whilst their previous license allowed AWS to leech off them, it's now been relicensed to prevent them from profiting off their future investments without compensating anything back.