However simply buying on market does not give the company...

However simply buying on market does not give the company working capital. You could say they are paying their own salaries out of their own pockets in exchange for shares.

And these director purchases have been completed already in the recent SPP so its (currently) not additional dilution.

It will however free up the (potential) near term future dilution by re-allocating these to "shareholder approved" from their current "non-shareholder approved" status.