Probably more time/hassle on their side
For cup finals when its an option, they use a third party they don't do it themselves
I always wonder why they don’t have a contract with either Royal Mail/any other courier to send away tickets out in a more risk free and efficient way than standard post.
I’m sure if they had such a deal the cost the company in question would charge them per envelope sent would be less than the price the club could charge on the ticketing page.
But I’m sure everyone would be happy enough paying it if it meant virtually ruling out tickets going astray which happens so often.
Club makes a few more quid, saves the hassle of organising duplicates for missing tickets, fans get tickets in plenty of time without having to wonder if they’ll actually turn up at all! Win-win