I love the way you say "It was only ever temporary" with such certainty based on...um....?
My office has sold off 2 of its 3 floors so there's no way we could ever all go back even if they wanted to us to, not that they've ever suggested it. Between my old colleagues, friends and siblings I know at least 10 people in different office jobs which were all office based in 2019 - none of us have been asked to go back full time, the most I've heard of is 2 days per week.
Apart from the obvious cost saving (which is hardly minor, you could be talking tens of thousands every year for some people just in terms of commuting, plus additional childcare, need for a full work wardrobe, etc), there's the obvious time savings, the obvious health savings (I haven't had to take one day off with cold/flu over the past 5 years, whereas I'd have 2 or 3 horrible colds/stomach bugs etc a year previously), the obvious quality of life savings, the environmental savings of fewer people commuting, the increased road safety savings of the same....