A lot of people who are in favour of some kind of intervention right now aren't necessarily going to want to turn this permanent.
For people who can't gain sufficient employment* this is an ongoing problem. The people who won't want to make it permanent are people who do not experience this type of instability on a regular basis.
It is interesting how our first thought to say "obviously this is temporary" rather than taking an empathetic look at what it must feel like all the time for a segment of the population (I'm just as guilty here).
* i.e. 1 job, 40 hours a week or less, that allows one to live a fulfilling life
A regular flow of such cheques compared to crisis stimulus cheques has a couple of advantages though:
- you don't have any ramp-up time, not even if you decide to up the amount in crisis time, as the system already exists
- you don't need to coordinate with multiple levels of governments, insurances, ... to hand out the checks
- regular UBI could offset/replace many struggling programs, from food assistance over child support to other financial aid, thus leading to less overhead costs
An awful lot of the wealth in Western states is based on this exploitation.