Increasing the width of the exit pathway doesn't increase the rate at which you can deal with the mountain of crap piling up at the end of the tunnel.
You sound like Elon Musk. "This problem seems easy. Clearly all existing TBMs suck so we'll just build a better TBM!"
It's really surprising to me that in 2019 the limiting factor in a billion/trillion dollars industry like transit is something that could be solved with a better conveyer belt.
To ask OP's question another way: many areas of technology and engineering have improved rapidly over the last decade or three. Have TBMs been keeping up?