The sad news is that those bots have been created by ordinal scammers.

I just checked one of the blocks mined by ViaBTC recently on blockchair.com and sorted the transactions by their fee rate. (Click here.)
In block number 822736, the required fee rate to get confirmation normally was 72 sat/vbyte. ViaBTC included 110 transactions with the fee rate of less than 70 sat/vbyte. 95 of them were 1 input - 1 output transactions sending 294, 330 or 546 satoshi paying 23 sat/vbyte.

I checked the 15 other transactions one by one. 11 of them were more than 500 vbytes in size and it's not possible that they have been submitted to ViaBTC free accelerator. 2 of them were confirmed with doing CPFP. In block 822,736, there are only 2 transactions that may have been confirmed with the help of ViaBTC free accelrator.