Why do we need other tools if there is UE4 / Unity?

Question

Game development

Hello. Always interested in this question. There are many engines for games, but the most popular units and ye4. Purely for curiosity, I began to surf google play and drive in information about each game, namely the engine on which this game was written. And often I was given out that C ++, Java was used. But after all, the games are simple, a unit would be suitable for their implementation, it’s easier, after all. Why do developers look to their own C++ / Java engines or ready-made ones in these languages?

Answer 1

1 You don't always need all the power of the engine
2 Sometimes, very rarely, the flexibility of the engine may not be enough
3 Developers may know their tool well, but not UE / Unity well
4 Reluctance to buy the engine or give part of the income to the creators of the engine
5 Efficiency, own engine or other highly specialized could be more efficient
And thousands of other reasons.