I think the answer here is that it is quite complicated to fix properly which is what I understand Monzo to be doing.
I may have got the wrong end of the stick somewhere (and I’ll almost certainly use some incorrect terminology along the way), but my understanding is that there’s a massive project going on to allow feed items to have multiple components. This is what will eventually enable the Coin Jar top-ups to be hidden, it’ll enable refunds or partial refunds to be collapsed into the original transaction and it’d allow a similar thing to happen for monzo.me payments splitting the bill.
From what I’ve gathered, this is a pretty major undertaking but it’ll definitely be worth it 