- Low GDP per-capita, offset by immense scale, which means the central government can mobilize massive resources for national projects, but municipal bodies are financially starved (municipal revenues in India are < 1% of total tax collections, for context it's 6% in South Africa and 10% in Brazil). Cities are completely dependent on the state for money, unlike countries where cities control their own property and commercial taxes, so they raise very little on their own, and states have multiple other priorities so cities never get as much money as they need.
- Leading off the previous point - executive power over cities is very fragmented, most authority rests with state chief ministers and state-appointed bureaucrats rather than empowered local mayors, so city planning is subordinate to state-level political priorities. City management itself is divided among uncoordinated state-level bodies (separate agencies for roads, water, power, and transit). There's a lot of accountability voids where something goes wrong and everybody thinks it's a different body's responsibility. The poor coordination also means you'll have things like a road laid on Monday, and on Wednesday the water authority digs it up to fix pipes underneath.
- The Indian constitution guarantees freedom to move and reside anywhere, so it's not legally possible to control rural to urban migration like China did with its Hukou system. E.g. Bangalore adds anywhere from 350k to 600k people a year almost entirely from internal migration. Much faster than housing, transit, and civic utilities can keep up with.
Things are getting better, although slowly and unevenly:
- Mass transit is expanding rapidly
- Door-to-door solid waste collection now reaches roughly 98% of urban wards (tougher than you would think because the unrestricted migration tends to create a lot of ad-hoc unplanned settlements on the outer parts of cities)
- The central government is working on allowing cities to issue municipal bonds to raise their own funds.
- Bangalore now (as of last year) has a single body called the Greater Bangalore Authority that has statutory oversight over previously uncoordinated agencies that handle water, transport, power, transit etc. Other state governments with major cities are watching to see how it plays out, and will likely copy + adapt it to their own major cities based on how it goes.
As for the rest of India, you can largely find the root causes of problems by tracing adverse selection effects among the elites that do remain, massive, conflicting vested interests and decades of horrible, incompetent policymaking.