Delhi kingdom did not pay any attention to give military training to a common man of the state. People were relaxed and enjoyed merry making which made military aggression finished.
The Delhi Sultanate could never recover from Muhammad bin Tughluq’s misrule and Timurlane’s pillaging, which happened mere decades later. The Sultanate was essentially no more.
After Muhammad bin Tughluq’s inept administration (which you can look up here: Shivaprasad Poovandur's answer to Muhammad bin Tughlaq undertook several experiments during his reign. What was the motivation behind these? What were their results?), the fate of the Sultanate changed. The economy was weak and a few provinces seceded to form independent or semi-independent kingdoms. Firuz Shah, Muhammad’s successor, did try to bring a reversal of fortunes, but his successors were caught up in a civil war. The tottering state of the Tughluq Sultanate seemed inviting to Timur and he invaded. Timur pillaged, reaved, killed infidels and carted off wealth from the subcontinent.
The Sayyids were mostly bound to the Timurids, often sending them a good part of the revenue as tribute. To be blunt, they were vassals of the Timurid Empire. The Delhi Sultanate ended with the Tughluq dynasty. The Sayyids encountered great resistance from the Turkic nobility of Delhi, to whom they were outsiders.