Why are scientists are developing alternative energy resources?

There are a lot of possibilities:  
We are going to (someday) run out of our current energy resources.  Much of the world's energy depends on fossil fuels, and those are finite resources.  Once they are used up, that's it.  An alternative energy source will have to be used.  Scientists know this, and they are trying to work ahead of the coming problem.  
They are curious.  Scientists are inquisitive people by nature, so looking in to new technology and energy resources is satisfying their curiosity.  
They are hoping to discover something amazing, patent it, and get rich.  A person that figured out an almost unlimited fuel source that is cheap and easy to use and maintain would likely become one of the richest people in history.  
They are environmentally conscious.  This is similar to #1, but it could be different in a key area -- pollution.  Fossil fuels and their burning pollutes a great deal.  Many new energy resources could be renewable and clean.  
https://www.eia.gov/energyexplained/renewable-sources/