They care, because the uncertainty itself is causing real problems, and the longer it goes on for, the worse it gets.
Take a business in France that sells widgets, a big chunk of which are currently sold in the UK. If a big UK company puts in an order for 10,000 custom widgets in 2 months, will they be able to actually supply them? Will their normal delivery company still be able to deliver? Will they need to do a mass of extra paperwork, which they won’t be compensated for? Will Sterling crash, so they get paid for with 20 Euros the owner had left from his last skiing trip, five stamps and an IOU?
In all seriousness, orders are being cancelled and money is being lost on both sides of the channel, just due to businesses not knowing how this is going to fall out. I suspect many businesses are currently just trying to delay agreeing to anything until they know which way things are going, but there’s a limit to how long they can do that. Plus, politically, with a significant proportion of UK MPs basically threatening to not pay up for agreements the country has made (framing it as the EU making unfair demands, rather than the UK trying to walk away from debts), letting the UK hang round, taking advantage of schemes that they may not actually pay their share for just isn’t viable.
Yes, the EU would prefer the UK called the whole thing off and started acting like a proper member again, but at the moment, my country is a liability, and it looks depressingly like the UK will shoot ourselves in the foot in a few weeks. The only other option the EU can give us is allowing us to dither about spreading chaos for a few months or even years, being neither truly in nor truly out, then shoot ourselves in the foot.
We’re acting like that mate who’s got way too far into the party drugs, who might just start a fight, or run out the restaurant without paying if you try to include him. Even if the rest of the group have been friends for years and they really miss who he used to be, no-one can really help, and they might make things worse trying. We need to sort ourselves out first.