Here are some reasons.
1) Renewable sources are variable in their delivery. Solar doesn't work when it's dark (or the panels covered with snow), and wind doesn't work when it isn't windy. So, you need other sources. Batteries just aren't a viable option on a large scale. They're heavy, expensive, have to be replaced periodically, and require rare metals mined by slaves in the worst part of the world - and we don't even have enough of those metals on the planet to go full electric. So you have to use fossil fuels, or, preferably, nuclear, as a baseline power source.
2) Neither solar nor wind reliably deliver power at anywhere close to their rated specifications. Even if they did, they require massive amounts of land and constant, reliable sunlight such as that found in the southwest US to deliver enough to offset conventional methods.
3) Delivery of power from renewables to their intended use location involves long, heavy wires, which substantially degrade the wattage being delivered over distance. So you lose a lot of the power you generate just moving it from point A to point B.
4) Solar and wind themselves are costly to build, and, again, use rare metals. They also have limited lifespans and have to be replaced, as they degrade over time. The third world is currently used as a giant dump for western renewables that have lost efficiency.
5) Solar and wind are not without their environmental problems, whether that be in taking up large amounts of land with panels, mining operations for materials to build and service and replace the equipment, destruction of bird and sea life with windmills, etc.
People concerned about the environment who have done the research will tell you that nuclear is the only way of out this mess. This is a fairly good and unbiased read if you're interested:
https://www.newyorker.com/tech/annal...-nuclear-power
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