Same reason people upgrade mundane cars to sometimes ridiculous levels of performance. Whether it's cost effective rarely comes into it. It's not uncommon to see the £2000 car with £20000 of upgrades and work outperformed by the untouched car that cost £10000. But I think it's very possible to take a £120 CM16, spend £100 on carefully selected parts and have it perform at least as well as a £350 rifle. It would arguably be a better Airsoft gun... Lighter, tough polymer that can take a few knocks... But given the choice between the Plain Jane that works really well or the average performing but high spec appearance, which do you choose?