It’s because of the rules around giving the British Armed Forces priority access to Shared Ownership. See section 3.2.1 here for details: https://www.gov.uk/guidance/capital-funding-guide/1-help-to-buy-shared-ownership

Please enter the amount of money that you can pay towards the property up front.

If you're using Right To Buy or Right To Acquire, please only let us know about the deposit you have personally. We will gather the details of your discount directly from the Housing Association or Local Authority.

Finally, if you’re remortgaging or staircasing, enter the amount of equity that you’ve already built up in your existing share. (And if you’ve got any more money to add, enter this information in the ‘Any other information box’ at the end of the questionnaire.)