I ask why because tons of other software achieve being free to use, free of charge, without preventing the software from being commercialised by a third-party. Why do they feel the need to prevent their software from being commercialized? The only reasonable answer seems to be jealousy.

It seems like you’re making assumptions. But who cares, what business is it of ours if they want to keep Defold free? Would you rather they charge for it? Proprietary and disallowing others to commercialize your software is the law’s default, and a perfectly valid choice. What does it matter why? Why are you feeling the need to judge?