That's pretty clearly because "free, quality public services to all" are really hard & expensive to deliver. Without prices & competition, they're prone to massive inefficiencies, over-provision or under-provision due to various political distortions, and resource- or agenda- capture by insider managers/public-employees/organized-lobbies.
Smaller, tightly-knit polities can often manage more-efficient public services. The two examples given in this article – "quality public housing" and "free public transport" – work well in some places!
But giant geographically, economically, ethnically diverse polities like the US have a much harder time. Public housing in the US sucks. Mass public transport here faces costs 5x as large in as other developed countries – due to the sclerotic interplay of dysfunctional bureaucracies, mercenary contractors, and powerful public employee unions. That is, those exact unions in the "Public Services International" federation which employs this op-ed writer. So of course she's arguing, "pay us first, and more, before spending more directly on the poor".
But the point of UBI, if it were to work as hoped, is to route around such non-poor middlemen – those who claim to be serving the poor, but rarely seem to reduce overall poverty. Cutting checks is comparatively easy to do, and most non-addicted adults can spend $X for their own welfare better than any supposedly altruistic outsider could spend the same $X.