Plugin purchase prices do not include hand-written code, even if it is only a few lines.
At commodity prices, and including 12 months of updates to new versions (including compatibility with future releases of WordPress and (where relevant) WooCommerce), and personal support, the margins when selling plugins are small. As a result, plugin sellers rely upon selling to many customers – and personal customisations are not economic (even if potentially useful for other customers).
You are, of course, welcome to send in ideas for new features. If you need a developer to customise for you, though, then we suggest Codeable – https://codeable.io – where there is a large marketplace of WordPress and WooCommerce experts offering their services.