>>718591439 (OP)
Developing engines in-house is a giant time and resource sink. On top of that, more time and resources would have to be spent to train new employees, developing documentation, and updating the engine for newer releases/platforms as well.
And even then, in-house engines don't guarantee the game is free of bugs or performance issues. Look at Capcom's newest Dragon's Dogma and Monster Hunter releases. Both of those games were made within their own proprietary engine and are full of performance issues.
NO engine is perfect. 10 years ago, it was Unity getting constantly shat on. If you pick an engine, it's on the dev to understand all its limitations and flaws and find ways to work around them. There is no be all end all to development in general.