The data that is used to generate the list comes from the Solana Foundation's Google bigtable instance in which all transactions ever processed by Solana are stored. This data is continuously read in and processed, and all transactions from the current and previous epoch are used to update this list, roughly once every 5 minutes.
Averaging data from the current and prior epoch has two benefits: one, it ensures that only validators with consistent performance problems end up on this list, and two, it ensures that validators stay on the list until they have shown that they have improved performance over roughly an epochs' worth of time.
For more details on the criteria that are used to determine inclusion in this list, see:
How does a validator end up on the poor performers list?
The motivation for this list is to provide incentive for validators to implement quality operations. The validators on this list are not performing well and a result the Solana network is not operating as quickly and reliably as it should. Validators should want to stay off of this list, to avoid embarrassment and reputational damage, which means that Solana will work better as bad performing validators improve their operations.