This is very likely a political decision. AZ has not honoured their "best effort" contract obligations, the company priortized UK deliveries to honour their other contract and Western Europeans are reluctant to take it because it's less well tolerated than mRNA vaccines and now the very rare blood clot issues. It's too bad, because vaccination rollouts are well behind schedule with less than 10% or so of the EU population vaccinated, while the UK has vaccinated almost everyone under 50 and at risk groups and are out of lockdown. Germany by contrast is imposing additional lockdown measures.

I got my first AZ shot it and I'm thankful it exists and really hope it works against the new variants. Maybe this is a chance for poorer countries like Ukraine, Moldova, the former Yugoslav republics and Albania to get their citizens vaccinated. Western Europe should probably donate part of their stocks to these countries through the Covax mechanism instead of letting it go to waste.