How to get people back in the office?
Some people prefer to work at the office, some prefer working remotely. I'm in the later group and it was a recurring conversation at my previous job. Beside forcing people to go back to the office which can result in the loss of the best performers (which might be the goal in some cases), there are a few things an employer can do to make returning to the office worthwhile to the workers.
Make them want to be there
That seems obvious, but it doesn't seem to be common practice. Make a great office with a great culture. Make it an environment where work gets done instead of one with way more distractions.
Also make sure they have great workstations. If they are better equipped at home than in the office, you're not making a great case for going.
Pay for transit
Going to the office isn't free for most people. They need to take their car or mass transit and if they don't already have a transit pass, it's extra money they have to spend. For me, each day at the office was about 500. Everyone's cost is going to be different, consider outright paying or subsidizing a flat amount for each day someone goes in the office.
Pay for lunch
People need to eat and it's much easier to prepare food at home than packing a lunch. Offering lunch (even if it's only one day a week) can be the nudge needed to get more people to come into the office.
Make the most of being in person
For all the bad arguments for going back in the office, there is one that is definitely true. There are some things that are just done better in person: socializing, whiteboarding and brainstorming sessions.
Why not make those in-office days about that? Schedule those events and sessions on those days so that workers really feel like they went to the office for a reason.
Just make sure that a day in the office is not simply the same day as they would be having at home, but more expensive and with more commuting. Offices with those perks don't need to convince people to come back, they want to be there.