To limit influence of bots on the economy as well as reducing burdens on the server by not having all the players explode the starting maps, which was in the announcement:

“We’ve come up with this initial access to prevent numerous Bot Accounts from the early stages of service and to provide a stable in-game environment to our users.”

The second part was my interpretation of it, but the first part is something worth caring.

And people have already did calculations to show that there’s really no ‘cost’ for the access itself, the hats/TP pretty much covers most if not all of the $ you spent, so it’s just you putting your wallet where your mouth is and show that you do support the game financially, not ‘oh I’ll pay later down the line’ bs that I’m pretty sure many people will say but never do.