It's been a long, hard slog for Metro Bank. To date, they've raised £641m (that's over $1bn) in investment and racked up total cumulative losses of over £130m ($220m).
And don't forget Metro didn't build their own platform - they outsourced all their technology.
Despite their apparent enthusiasm (see links at the bottom of this post), I don't think VCs are ready to sink over a billion dollars into a single startup, even if it is a bank. They're looking for billion-dollar exits like Facebook and Whatsapp, not a $1bn investment with a $100+bn exit.