There's also the issue of licensing. For something like UE3, you have to pay for each console platform SKU. I recall the UE3 license is like $500,000, so that's $1,000,000 just to be allowed to release it for the XB1 and PS4. Then pay employees for a year or two to port and integrate as chances are, the integration from when ME was on the XBox 360/PS3 is much different to the XB1/PS4 version of UE3.
Also, if you've noticed, EA is pushing Frostbyte as the engine of choice since it's made internally, reducing the reliance on an external provider like Epic.
Not saying it's impossible (ME1 on PS3 anyone?), but the return on investment isn't actually looking that great at this point, especially when as mentioned, the PC version is handling the future compatibility just fine.