Unity has 5200+ employees and a net worth of 4.8 billion USD
Lexaloffle games has 2 employees and an unknown net worth.
There's an obvious reason why one is free to use, and the other is not. Unity can afford to make their engine free to use for personal use, they have massive contracts with commercial game development studios & make all their income from them. Lexaloffle Games needs money to put food on the table while the 2 of them work on the engine.