Trying to introduce a new product that competes directly head to head with an existing one is seldom the best strategy, and the van/minivan segment is currently underserved.
If VW can make a compelling people and stuff transporter EV - especially if they can make something that's as easy to use and capable as a minivan while avoiding the minivan stigma - then they can likely tap in to a bunch of market potential that Tesla hasn't gotten to. That'd let them sell a bunch of cars even if they can't match Tesla point for point on efficiency, price, charging, and autonomy - as long as the car is attractive on its own merits.
I actually think it's a rather good idea on their part - at least if they execute it well and bring it with a 200+ mile range and good fast charging.
And, as S'toon said, they're planning to build a bunch of related EVs over the next few years in various segments - maybe they'll get the sort of use out of their skateboard that Tesla was talking about years ago but never really managed so far.