It’s a simple business case analysis - not notably different from, for example, a s137 application.
PC may have land which can be allocated to GYO allotments but that’s not to say PC has to organise, administrate and maintain the facility.
‘Someone’ - logically one who desires an allotment - needs to formulate a needs analysis which identifies and demonstrates sufficient interest to make the project viable (number of participants x rent = annual income), Then they need to constitute a ‘group’ to organise and administer routine maintenance, rental collection and terms & conditions of membership.
That type of detail should be presented to PC so that PC can identify up front costs and balance these against the likely timeframe for financial recovery and the general ‘benefit’ to the community
Then maybe a rational decision might be made. There may be scope for PC financial subsidy but only if the number of allotmenteers equates to a significant proportion of the community. If not then the PC may be subsidising a relatively small portion of the community and subject to challenge/criticism.
As a general concept - most groups / organisations / facilities should aim to be financially self sustaining. If not, there needs to be a watertight argument that the subsidy equates to significant community gain.