If you have no idea the size of the transactions, then knowing the total number tells you nothing useful. In our example above, 1 "big" transaction can take up as much space in a block as ~150 "small" transactions. Using the numbers above, if you tell me there are 400 unconfirmed transactions with a fee above 10 sats/vByte, I don't know if that means a fee of 10 sats/vByte puts me 0.1 MB from the tip and likely to get in the next block, or if I'm ~15 MB from the tip and am going to be waiting hours.
That's why the third chart (Mempool Size in MB) as mentioned by figmentofmyass is far more useful than total number of unconfirmed transactions.