I think it aim for bots.
If you start telling people where is the limit, then bot can collect data every day without reaching the limit.
With an unknown limit, there is a lot of extra work to do for them to work well.
I remember a thread where a random player come into the forum saying something around 'hi, i collected some data from top players, i saw X, Y, Z. I hope that's useful!' and the previous admin answering they saw some increase of traffic and tried to track it/limiting it during weeks or months. [remember that admin doesn't knew what caused those extra traffic from the website]
And I believe that's when he added a limit.