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To begin with, the things you need for calisthenics do not burn a hole in your pocket. Getting a home gym is drastically more expensive than getting the basic calisthenics equipment.
Even if you want to buy barbells, weight plates, benches, etc., it will cost a lot. On top of that, and often the bigger impediment is the need for a dedicated space. You can, however, do as many push-ups as you want in your drawing room.
The key reason behind the efficiency and popularity of calisthenics is the ease of doing it. We do not mean that bodyweight exercises are easy.
On the contrary, they are often more difficult and require more balance. What we mean is that you can get a bodyweight workout anywhere.
You do not need a gym, a fitness studio, or even a park. All you need is your body and a few basic things like bars, benches, tools, etc.