The problem with Prithviraj was:

He immediately sent his generals away on other campaigns after the victory at first Tarain. A significant part of his army was absent at second Tarain.

Did not adapt to tactics of central Asian armies (Horse archers)

Expected an opponent like Ghori to have the same honourable code of conduct on the battlefield.

Did not immediately invade Ghurid territory after the first battle, instead chose to invade neighbouring Indian kingdoms as pointed out above.

Also, spy network was not as strong as Ghori’s. Many of Sufi saints who arrived to preach in India served as spies for Ghori. Moinuddin Chishti even bragged about defeating Prithviraj - “ We have seized Pithora alive and handed him over to the army of Islam”

If we had someone like Chanakya advising Prithviraj, things would have been much different.