They are to force you to behave in a manner that's acceptable to the authorities.
A recent scheme in Westgate-on-Sea included 'changes to the parking bays, to encourage walking and cycling... using parklets, planters and bolted down bollards (delineators) to reallocate road space.' This was done 'to promote social distancing and increase walking and cycling opportunities.'
The scheme was eventually upended after intervention from 'local KCC members, the town council and the local MP.' But the local authorities will continue to impose them as they 'give us the opportunity to lock in some of positive travel patterns we have seen during the pandemic' [KCC's grammatical error, not mine].
https://www.kent.gov.uk/roads-and-travel/road-projects/in-progress-road-projects/emergency-active-travel-fund-schemes/highway-emergency-active-travel-fund-projects#tab-65