Do they? Most businesses in the real world have to generate cash or they fold. Venture capital can keep small startups going far beyond their useful life.
But how many startups receive any appreciable amount of VC money? How many are operating on the savings of the founder(s) and/or money from family and friends rounds? How many founders are going into personal debt to fund their startup?
And how many of them that do raise funds go crazy on a hiring spree once they get any remotely reasonable funding, while not having a functional product or a remotely sustainable user base?
According to Crunchbase only 1 in 3 startups even make it to Series A (between 2011 and 2018, the % was fairly consistent each year)
Looking at "funding data from around 15,600 U.S.-based technology companies founded between 2003 and 2013" TechCrunch comes to the conclusion that only about 40% that close a Pre-Series A round make it to a Series A.
Most businesses can get loans, including unviable ones, by either
1. Burning existing equity: Owner uses own house as security to get loan, common story
2. Political pressure to get loans: This is how zombie companies are born, and they are very common outside of anglo saxon countries.
I would not say startups are subject to more or less business discipline compared to normal companies of the same caliber. Your average tech startup founder has a lot more resources and credentials to burn in emergencies compared to an immigrant starting up a restaurant, so it has to be a like for like comparison.
Do they? Most businesses in the real world have to generate cash or they fold. Venture capital can keep small startups going far beyond their useful life.