Because it’s easy to set targets and measure them while in the gym, but it’s not easy to fit that kind of exercise into the day to day.

People often live too close to work for the bike ride to really be considered exercise, or too far, where they couldn’t feasibly fit it into their day.

I get it, doing exercise for free seems like a no-brainier, but not everyone’s life and exercise needs converge neatly to make it easy.

Because the outside air is polluted and having to wear a air filter while exercising is unpleasant.

Because I have to watch out for traffic and pedestrians outside, and driving to a cycling/running path takes about 15 minutes anyway.

Because looking at healthy, fit people exercising gives me more motivation to get in shape.

Because I can devote more attention to my audiobooks than if I was exercising on the streets.

Because the gym is in my apartment complex, so I just go downstairs and walk 2 minutes to the gym.

There's another article on the front page that pollution increases the risk of either getting or accelerating Alzheimers, I forget which. Either way, if you live in a city, getting aerobic exercise out of doors is probably counter-productive when done for the purpose of cleaning your brain. In that case, indoors at a gym might be an option, if it's well ventilated and fresh air is filtered first.own.

You can watch TV on a treadmill, something that is much harder (and more dangerous) while running outside.

Sometimes the weather blows.

Probably for the same reason people go to the gym to exercise yet don't do any pushups at home: we pathologically avoid exercise, so we often must compartmentalize it away from our life to actually do it.