the reason is probably because the government decided herd immunity was the solution - just let everybody get it and boom, we're cured.
Problem is, it is not gone, it is just as contagious as it was 6 months ago. So, we have 2 options - either stay in perpetual lockdown, or start mingling again. If we start mingling now, we can infect more people while the hospitals are mostly coping. If we wait until September, send every kid back to school and open all the shops, cafes, pubs, gyms etc. then we risk another peak in winter, which will be bloody awful.