One of the problems being discussed, is that ordinary people cannot afford the most basic offers in the market. (See Ipsil's posts) This is partly because the top 1% earners are buying and then hoarding, all means of gaining market power. (See for instance, Silicon Valley, and realestate.)
To combat this snowballing effect, you need to prevent the 1% from escaping reality through capital gains. (or rather, force the rest of the market to move upward with them.) The further the 1% climbs the slope, the more profound the impact of the rest of the market being left behind. (EG, Google or Apple can afford realestate in silicon valley, but no ordinary person ever could, as the costs are driven ever upward by demand and endlessly deep pockets.) There still isn't really a limit to how much a 1%er can earn, just that the more they earn (Compared to the median income), the higher the UBI needs to be to combat the problem. (It assures people can still buy basic things, like houses.)
I am not naive, there are not unlimited houses out there-- but it DOES put the brakes on for people buying up properties, driving up demand, then selling at high rates. This is because the effective power of their investment is diminished by their money grubbing (collectively), while non-moneygrubbers still have buying power in the market. It effectively prevents shutting smaller people out, via sheer force of capital. This is because as they make it more unlivable (and get richer in the process), everyone else gets more money to combat their hoarding. The less they hoard, the more money is useful for them, because other people get paid less.
re: Max
The "Above UBI goal" thing for working is intended for people who work for somebody else, either because they lack an intrinsic skill, or lack the desire comittment to self-betterment through freeing their time for themselves, but most specifically-- for people who are just plain greedy, and want more. The idea is that the UBI is an enabler to remove burdens of meeting and sustaining a comfortably livable life (all on its own), but if you want to own something clearly luxurious, the presence of the UBI is going to make luxurious goods more difficult to obtain. You either have to save money, OR, get gainful employment. It is intended to be presented in a fashion that a 1% understands, not that a normal person would think like. To a 1%er, getting "more" is a noble goal in and of itself.
By its existence, that greed can still be harnessed to leverage group labor for large projects that a single person could not achieve. Things like constructing highways and the like. The margins of such businesses can be lower, because the expenses are lower, because everyone already has healthcare and a livable wage (even if they dont show up to work.) People WANT more, so they still come to work, because working for somebody else is EASIER than self-betterment.
There will be no shortage of people who use the UBI to self better themselves, such as perhaps, you might make and sell wooden durable goods. (You do it mainly for the enjoyment of the process, but something useful is still created, and probably sold. the UBI enables you to add that offering to the market at very low risk to yourself.) There will likewise be no shortage of people who do not do that, and would rather work for somebody else. (In which case, the UBI makes it easier for people to hire others, because the costs to entry are much lower. It also makes workers happier in general, because they can be more picky about who they work for, and what kind of work they do.)