But you still need to keep enough there to not have to rely on potential members joining and paying on time.
Totally agree, and I suspect they've budgeted for X number of members which is a figure they're confident of reaching.
The only real downside to requiring members to pay in full by a certain date is the potential number of customers they would lose by not offering an option for more incremental payments.
But it's a fact that people are far more likely to pay for things like this (football club memberships) in the 2 or 3 months prior to Christmas. Interestingly, football club memberships fill the same role for consumers as signing up as paying members of charity organisations.
Case in point is all the charity panhandlers flooding the streets of city centres at the moment, trying to sign people up for 12 month financial commitments to this or that charity. You'll be lucky to see any at all the rest of the year, except for a little burst of guilt-for-sale around the end of the financial year (because it's tax deductable).
But as far as I know, football club memberships aren't a tax deduction.