Captcha purpose is to know you are human.
They allow no captcha if people just deposit a fairly modest amount, considering the giant amount BTC has risen over the years despite being uncertain week to week you arent really doing yourself any harm to gamble the small amount helping the company rather then trying to knock down the walls they put up to keep out an army of bots that arent real customers.
Put it this way if you succeed in creating a perfect bot to collect and never actually participate in this site, the site wont exist as its not worth their while bothering any longer. Did you really win by doing that or was it just selfish short sighted a momentary victory before you must move onto the next site and attack that similarly. BTC already goes up alot so I cant see all this trouble to not use it properly.
By accident not any great wisdom, I used to sign up and use all kinds of sites in 2013 when price was $100 and one site I forgot a tiny little balance. Came back in 2018 to that site and it paid for my whole pc setup, I kinda earnt it and I kinda just was lucky but the big deal was some site was reliable enough to store that balance the whole time. Do I really want to see Freebitco disappear, obviously not and it really doesnt benefit any of us to try these measures to 'get around' its normal operation. Its probably true the entire BTC ecosystem benefits from the variety but also longevity of some players, ie. the price gains from usability, reliability etc.
Price worked against me this month on May price guess, cant be lucky every time and was unsure so not a big bet.