It is widely observed that many people work far more than is necessary to supply their basic necessities, because people's desires don't tend to end with those needs.
You may have quite limited desires, but there is no evidence that that is true of humans generally.
Which serves to further increase inflation.
So you increase the amount more, and shortly thereafter inflation increases more again.
And so you increase the amount again, and so on, and so on until suddenly you have hyperinflation and your economy collapses, see for example the Weimar Republic, Zimbabwe, or any of a dozen other examples throughout history.
Most of the proposals I've heard of UBI / negative income tax are good supplements but don't completely replace work-based income. $1000/month per adult is among the largest benefit I've heard.
That's great, but if a significant number of people feel that way, then there is a noticeable loss of productivity in the economy as say 35% of people are not producing anything of economic value. That impacts tax revenue. It probably also means there is work not getting done, like the stuff nobody wants to do.
I'm pretty sure there have been various studies all but disproving the "common sense" notions people have about UBI and laziness. Or the fundamental idea that if you don't make it hard on poor people they won't do anything of value. Or that poor people are lazy, and that they are poor because they are lazy. Etc, etc, etc.
Which serves as a reason to regularly increase the amount.
“UBI doesn't make people not want to work at all“
Speak for yourself. Work is a means to an end. I have no desire to work if basic income takes care of my basic necessities. I have no intrinsic desire to get up every day at the same time and do what my employer tells me to do. And to be clear, when I say work I mean the necessity of doing things in exchange for money. Cultivating my garden, writing software nobody uses, or music nobody pays for, isn’t what I mean by work.