I may be wrong, but the Unreal Engine became so popular because it was "easy" to use, Epic provided a lot of tech support and, during the transition from SD to the HD era, the PC origins of the engine made it better prepared to deal with 720 and even 1080p resolutions.
Also, as of late, they've changed their revenue system to make it more attractive to publishers and small studios.
But well, Godot may be good, but I'm not usre how many 2D games were build with UE to begin with. Unity seemed to be the one with more chances to compete with Epic.
Please excuse my bad English.
Currently gaming on a PC with an i5-4670k@stock (for now), 16Gb RAM 1600 MHz and a GTX 1070
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