Although that might indeed have been part of the reason in some cases, the real reason is always money.

They have all those big office buildings around, which had a cost and are worth some real money today. If they allow those to be left empty, it is just a question of time before they start losing value and real estate investment would come crashing, a lot of money would disappear from the market that way. The inconvenience of an employee is worth much less than whatever stupid capital gains they might be able to get on their business real estate investments.