Recently according to my research I noticed most digital currencies use more than one network for transactions why is this so
1st: Define 'network'...
I assume you mean different servers & nodes for each different coin and its associated blockchain?
If so - yes and for what should be an obvious reason: They are totally different coins/tokens created by different groups/companies and are serving different markets...
Since this deals with not just
BTC but also the plethora of altcoins this really belongs in
the Beginners & Help area or General Discussion area. Not here as this section is exclusively for Bitcoin. Requesting the mods move it there.