for a few reasons
I think it was explained by Tom somewhere that it costs about £4 /year (from memory) to service the crowd cube shareholders - so somebody putting in a tenner would actually cost Monzo money over 5 years rather than raise any finance to carry on the development of the business
Its far far ‘easier’ to raise 20m from a single investor than 20m at a tenner a time from 2 m investors - not so sure you would prise 20m from my hands in one hit 
:-0 but i suppose its all relative to what you’ve got Tom and team do seem to have a knack of getting big hitters to back them
what happens if you put your major investor off saying we’re giving 70m to minor investors and only 10m is taken up - you then need to go back cap in hand to major investor who will want more equity because they now know you couldn’t raise the required capital elsewhere
you would never know until the crowd fund was over that you got the finance that you wanted , but the whole world would know how much interest there was in your business - this could obvs go either - way good or bad
You are “only” allowed to raise €5m / year (i think) with crowd funding without a prospectus
- toms previous post - it was £4 / year
- Next opportunity to crowdfund?