We don't.
We haven't been in 'lockdown' since March, but deaths and hospitalisations have only started to really grow since mid July. There are clearly restrictions we can impose which are effective without a complete lockdown.
Okay, so we go back into the form of restrictions that we saw from April to June?
That's all well and good, but that also cripples huge sections of business.
Hospitality, the industry probably hit the most by this, can't rely on outdoor trade in the winter months as it could (well, kind of) in the spring and summer.
Events that are just getting up and going again will have to be cancelled, as all of those are indoors. The music and entertainment and arts have really been hit hard by this. Theatres and venues were already going bust before COVID, so God knows what it'll be like now.
So it may not be a complete lockdown, but it still cripples a lot of businesses and risks jobs etc. Then you take into account the whole people not even being able to see each other thing. Not being allowed to go into other people's homes.
Did you enjoy your day at the cricket last week? I enjoyed mine. I can't wait to hopefully get to a gig I've had booked for two years now, when it comes around in late October. People need to be able to live their lives or what's the bloody point. Just keep everything in a state of limbo and let's all wait to die.
Edit: Btw, I think the above is what will happen, I actually agree with you. I don't think it should, but it's definitely foreseeable.