The answer is simple.
Miners always try to maximize their profit.
a) The block can be filled 50% with tx at 2sat/vb, the next tx in order at 1.99sat/vb will cover another 30% of the space but the next two one each at 1.98sat/vb are 25% so they would either both fit or not, higher revenue for miners or fee order?
They will include one of the transactions paying 1.98 sat/vbyte and
a transaction
(s) with lower fee rate to fill the block as much as much possible and maximize their profit.
All my answers I found would point to the miner going by profitability but then why do some pools still mine like this is not of concern and still have empty blocks when they could choose some small tx from the mempool to fill them up?
That's just because some miners have not changed their policy rules
yet. More and more miners will accept such transactions in the future.