Why does it take 7 days to withdraw the funds bridging from L2 to L1?

First of all, please note that a withdrawal from L2 to L1 takes at least 7 days to be completed.

After submitting a withdrawal you will see an estimated ETA next to your transaction and the number of days you have left until the withdrawal completes.

The 7-day window is set based on the agreement in the Ethereum community on how long a censorship attack against Ethereum itself could last. We’ve advocated that we think a shorter window would be safe, but the general consensus has been that it’s best to stick with the current setup. Hopefully, there will be an agreement to lower this at some point, but there are no plans to do so at the moment.