How come mobile manufacturers don't create batteries that don't need recharging or at least have a much longer battery life than they already do?

expensive experiment, last try was Hydrogen cell batteries but still expensive 

because of mobile dimension, Size and weight factors.

They did it years ago. Remember Nokia 6310? Or Ericsson ? It used to work for days without recharging. Te modern smartphones uses very powerful CPU and GPU, lots of sensors etc.... and all of these eating buttery very fast.  

The life of any battery depends upon the ampere hour (Ah). Most of the smart phones consumes a lot of power. When you purchase the mobile next times then look for more ampere hours  for the battery provided with the Phone. 

The recent technology - Lithium ion batteries - is very limited i.e. if you increase the battery capacity too much or if you charge it too fast it becomes unstable and might explode. other technologies are still under development and are not marketable yet.

For a longer life Mobile devices this is possible, but manufacturers are thinking and looking for an easy handheld device, that should not be heavy while roaming.

however some of them started with solar cover but this is not really effective as the power consumption of phone hourly is about 30 to 50 mAh, more than solar charging specially when you are in office for more than 8 hours. Other industrials are proposing like recharging bags, hats and some other clothes in order to easy the distribution of weight coming from the external batteries.

longer life charging cell is the trend for researchers, but also wireless charging is started to be also available in public area.

I guess also from the consumer itself, should be more wiser while using his handheld, process of  video streaming, video calls and hotspot tethering consume more than half of the daily phone charge.