It is not all just about "financial sense". For some, it's about pushing beyond the traditional limits of airguns that is thrilling. It's about extending their PCPs and their own shooting skills to target ranges that was once thought near impossible with an airgun. Just like in the powder burner world, you can buy cheap surplus ammo, or you can buy and shoot the latest A-tip ballistic bullets at 5-10x the price of surplus ammo. Does the pest care that you are using surplus ammo with 1.5 inch grouping versus using ballistic tipped ammo with 1/2 inch groupings with a phenomenal BC? No, but it matters to some shooters - personal pride and satisfaction. Time is valuable, as someone stated rightly above. Might as well extract the most fun and enjoyment while you are at it even if is costs a little bit more.
Same argument could be made about having a beater car that works just as well as a German Porsche or Italian Ferrari for getting you from point A to point B, but until you have driven one...