If I accept the offer, I'd rather get 1 BTC without risking anything, because that's more than enough that I can get, because collecting 1 BTC is very difficult for me personally.
Same here, I won't be greedy aiming for higher amount. 1BTC is a sure fund in hand. I would rather choose the one that is 100% claimable than a higher amount but need to gamble. Gambling has random results, no matter how high the odds is we are not sure whether we will win or not. Just take a dice with 98% chance of winning having a result of consecutive losses. what more the 50% chance? I will not risk the 1 BTC for 5 BTC. It is a good enough fund to setup a business that can yield more than 5 BTC if becomes successful.
In a game of chance there is no guarantee that you can 100% achieve it. Even a parlay in sports betting does not guarantee a 100% winning result, let alone the chance of upset in every match. Your calculation is an assumption that the result of the match goes your way, but what if it does not go your way?
I think it is much better to take 1 BTC and gamble it to become 5 BTC, than choosing 5 BTC where we have a chance of losing even before we have the grasp of the fund. At least with 1 BTC as the initial bankroll, a 5x of the bankroll is somehow doable even with medium luck.