Expanding a Bit on this:

● Delhi/Delhika hasn't really been "Important" city from Hindu Civilizational perspective (Post Mahabharat). It was more important for Invading k2as because of it's proximity to Punjab, from where they could hit and Run.
(1/n) https://twitter.com/_ugra_/status/1354006296140382208

So which cities were important?

Ayodhya, In Scriptures has been Described as a city Built by Vishvakarma Himself for the Pleasure of Descendants of Raghu.

Kannauj was So Important that 3 Mega Powers (Pratihar, Pala, Rashtrakutas) Fought each other to control it.
(2/n)

Area In and Around Magadh has seen the Glorious Rule of Both Mauryas and Guptas.

Varanasi witnessed Not 1, but 10 Ashvamedh Yajnas, performed by Naga Kings (there's still a Ghat Named दशाश्वमेध)

Satvahanas, who were Termed as Lord of 3 seas, Had Rich and Prosperous Pratisthana (Paithan) and Amravati as Capital.

Riches of Vijayanagara aren't Hidden from Anyone, But few People know That Shankaracharya Shri Vidyaranya Propitiated Goddess on the Foundation of Vijayanagar.

Anahilwada (modern day Patan, Gujrat) was the Capital of Chaulukyas.
It is estimated that in year 1000AD, it was the 10th largest city in the WORLD.

K2a Historians Described the Riches Alauddin looted from here.

About Ujjain, I don't think I need to say much.

Vidisha was An Important center of Trade and Formed Capital of Eastern Malwa.

The Famed Chandelas of Jejakabhukti (Bundelkhand) had Khajuraho and Kalinjar as Capital, whose Fort was Envied By k2a Historians.

I Can go on and On. The list is Endless. Point is this:

Delhi,As Capital, Is good for Invader as An Escape Route, Not For Its own Citizens.

*End*