Today we are going to learn There are many reasons behind it. May be package you are searching for not available in the Termux repository.

You may need to correct the spelling for the particular package name or that package has not been added to the repository list. Today we are going to add all the possible packages for Termux. These are the available package list container for some extra programs for Termux. You can also install Black Termux to add some more packages and follow the commands below: Ensure that you already have installed the latest version of Termux and Termux API from the F-droid app store (provide all the permissions to termux and Termux API manually).

$ pkg update && pkg upgrade 
#Provide storage permissions
$ termux-setup-storage

#Locate package in termux
$ termux-change-repo
or
$ nano $PREFIX/etc/aptsources.list
$ pkg list-all |grep "package name you want to install"
Or install some more packages containers types. 
$ pkg install unstable-repo
$ pkg install x11-repo
$ pkg install root-repo
$ pkg install science-repo
$ pkg install game-repo
$ curl -LO https://its-pointless.github.io/setup-pointless-repo.sh
$ bash setup-pointless-repo.sh

#Check
$ ls ~/storage/shared

[ Final step ]
Update and upgrade 
$ pkg update && pkg upgrade -y

#This will also fix unable to locate package python on Termux
$ apt install python
$ apt install ruby
$ apt install php
$ apt install git
$ apt install curl
$ apt install wget
$ apt install vim
$ apt install tor

You can install termux black it has more Hacking repositories.