Same here. Even walking 20 minutes every morning is nice to start a day. Now working from home requires some discipline, and I compensate it with doing a spontaneous jogging during a day.

I think purpose. It's easy to take it as a perk that you can ride your bike for 30 min and get "free" exercise while you go to work. It's a bit different mindset to ride your bike just for the sake of exercising and not having a bigger goal behind it.

It's easy to make the switch though, I did it :)

Much simpler solution as suggested by other commenters: Simply get into the habit of riding a quick 30 minute loop on the bike before working at home. Biking or running just for the sake of exercise is a completely normal thing to do and I don't see why it has to be justified by a specific purpose like commuting.