1. They don’t need the full building anymore.
2. Building ownership requires maintenance which is either inefficient to have on staff or which you outsource anyways.
3. owning the building most likely means you are depreciating that cost over 27 years the end of which you have an old building. Renting the space means you can deduct the rent in full as an expense and you can move easily when the space is no longer up to snuff.

In addition to tax reasons, and maintenance reasons, it can also be a cashflow solution. If you own a million dollar building, then that million dollars is "stuck" there. If you sell the million dollar building, then lease the space back for fifty thousand a year, you have 950k to spend on buying new equipment, hiring new people, paying salaries, etc.

Even better, as others have said, if you only need part of the building, you can pay less in rent since the new building owner can collect rent from other tenants.

It is also a great way to reduce how much the company owns, and how much it owes, which makes it easier to be acquired by a larger company (such as Paramount).

Note that this also can be done if the value of the property changes significantly.

For many companies, renting is a better tax situation because they can claim rent as a business expense that means their net profit (the number that is actually taxed) is much lower. So even if a company wants to own a building, the owners will create a separate business that owns the building and rent it from their other business.

Why does someone who owns a car sells the car and takes a cab or rents a car when they need it? Among many reasons could be that they are downsizing or cost of ownership is higher than for hire/renting.

Flexibility. I have a business owner as a client. He wanted to retire. He owned 2 businesses: a hardware store and the company that owned the land the store was on. Upon retirement, he sold his hardware store. The new owners paid a lump sum in cash and that was that. However, they now have to pay rent to my client to the tune of $10,000/month. Included in the sale was a lifetime lease agreement. He'll have that $10k/month as long as he shall live.

If he owned the store and the land as one company sure his sale proceeds would've been greater, but probably not to the same extent that sales proceeds plus $120k/yr in income will result in.

Companies usually buy bigger spaces than they need. They anticipate growth, so you buy bigger. It would be common to rent the extra space out, as this is only going to be temporary-- you're not in the business of being a landlord, so temporary before you move yourself in there.

But what if you end up not needing the space? Well, again you're not in the business of being a landlord, you're better off just selling the building and renting only exactly what you need. This allows you more flexibility.

Lastly, in the US there are some often significant tax benefits of leasing vs. owning (less than ELI5: It actually common for some business to have someone, like a owner buy the building and rent it back to the company, or have a shell company buy the building and lease it back)

Short term gains. You have just bought say, Woolworths, loaded the debt onto the company. You then sell off the freeholds and rent them back. Bang, huge profits for the new owners . Run it into the ground, go bankrupt but walk away a lot richer.