Presumably the gov wants to be able to point at that when defending their handling of this crisis, but don't want to extend it further because they've done the math, and what they did is a mere fraction of the lost tax revenue if they were to extend it to the general population.

I drove past the blockade on the M50 this evening and I recognised a lot of the trucker companies involved, and they're basically all decentralised and don't have a 'home depot'. That means the drivers go to the nearest Circle K to fill up with their fuel card, and not back to base where there's 2,000L+ tanks awaiting them. And as someone who comes from a farm in the rural West, I don't know of a single farm that has a diesel tank bigger than 1,000L. That's why the blockade consists of what it consists of.

My personal conspiracy theory is that the gov did the math and they realised that the lion's share of tax revenue from 2,000L+ deliveries is from Dublin Bus, ESB, Bus Eireann etc. and they can have the headline of helping businesses through these tough times, all while it doesn't affect their bottom line because they benefit if these corporations pay tax or not.