I think colonialism gets blamed because it's the closest external thing in time that can be blamed. Counterexamples like Singapore get bandied around, but the difference between a state the size of Singapore and something like India or Bangladesh is staggering enough to make the comparison essentially useless.
It is an interesting thought experiment to imagine what the consequences would have been of a more gradual transition away from British rule in the Indian subcontinent. My imperfect amateur historical study makes me think it would have been a net positive, but potentially would have led to partition into at least 5-6 different independent states before they did leave for good.