Why doesn't the "watch" command work on an alias?

So I've made my customized alias command and tried to use it with alias, but my alias was not recognized while concatenated with the watch command.

So I tried to make a thread of it and fortunately, this one helped me out.

But what is the reason for this?

I've created an alias in my .bashrc which works perfectly fine.

alias gpu='sensors nouveau-pci-0100'
alias cpu='sensors coretemp-isa-0000'

and when I concatenate watch and gpu like this:

watch GPU

I get this below every 2 seconds:

sh: 1: gpu: not found

And I solved it regarding the mentioned thread above like this:

alias = watchh='watch '
watchh gpu

But why does this happen? Why can' It use my surely defined alias command?

My guess is it is something about the user because I've gone root once and I couldn't use my alias but I surely need an expert to answer this.

The watch command does not locate aliases, only commands in your search path. As an alternative, define gpu and cpu as shell scripts instead of aliases and place them in your search path. Then your watch gpu and watch cpu commands will work fine.

For example, if $HOME/bin is a directory in your search path, create a file $HOME/bin/gpu containing the line:

sensors nouveau-pci-0100

Make the file executable:

$ chmod +x $HOME/bin/gpu

and you're ready to go!

$ watch gpu

Then do the same for cpu.