Why a limit on the total number of challenges of 250 instead a day limit of 1 challenge per day?

You can continue after 250 challenges, but you will just not get any more points.

Ok. I thought the fun was to do challenges with other people but the fun is really to get points and badges. The challenge with others is in reality secondary.

The issue is the number of points. With 1 challenge per day you will get up to 730 points per year. That will be exploited just as the unlimited challenges were. In just 5 years you will have 3650 points just by doing challenges which is half way to level 9. Together with the other repeatable badges and normal badges you will be a level 10 and then lots of people will be maxed out again.

Thanks for your calculation, but it is not correct. In your calculation you do not assume that you will lose, so who knows how quickly you will reach level 9, but this is not the point. The point I want to make is that it helps me to give that little bit extra if I know that I will be rewarded for it with a badge or points, just for that little bit of extra motivation.

A challenge per day was just an example. Maybe you can only give 1 point per challenge won or you can only compete against people of the same level. I'm just saying things. It's just a shame that when you get to 250 there is no motivation to win a challenge. Yes for fun but that doesn't work for me and is think for a lot of people.

You must always consider that all systems will be exploited. That is why the limit was added.