This is something Kishi never fully explained.
How does Susanoo get stronger?
Is it the amount of Chakra you put into it or does it just get stronger because of EMS, or is it a result of being more experienced at using it?
Common logic and Karin, tells us it's chakra + life force.
Why? Look at it... Karin always commented about his chakra while Sasuke's Susano'o got stronger, as well, when Kakashi engages him she says that she might've healed him a bit but it's too much. And we know that her healing acts like a life force factor given the fact she's an Uzumaki. And when she stopped healing him, due to him stabbing her, when once more his chakra got even colder, the third stage of Susano'o appeared, however, given his deteriorated health situation (life force) his Susano'o vanished quickly thus concluding that Susano'o => chakra + user's life force.
Lol seriously. Sasuke was in pain from using MS Susanoo and Chojuro used an attack that stored up massive amount of chakra. Notice it only sent Sasuke flying not breaking it.
And that very well explains the life force part.
And stored a massive ammount, but we don't know how massive. It would've been something similar to Tsunade's, It would've been already broken.
However, I think you didn't get my post. Madara has a benefit with Susano'o, while Sasuke doesn't. That's why it might seem more resilient than Sasuke's.