tl;dr - easy to hit revenues faster and get paying clients, like all IT services companies.
Saas is 70-80% like service industry. Similar common demand products, same clients (what an Infosys does), except it packages each 'client project' to market better and let client get the solution bit faster.
Demand for services at low cost is huge worldwide. Tech salaries are lowest in the world, and hence easy to build solutions in India and sell in US, Europe with sales offices there like how all the WITCH are the biggest tech listed companies in India. Most saas startups you see will be in CRM, marketing, sales, ITSM, Data Ops, Infra segments and there will always be some segment of client company (maturity, size, industry wise and all) who have unmet needs. Founders have to work finindg them, shape their offering and start making money soon. Unlike consumer products which are super hard to monetize.
P.S. Saas companies are still service companies as the last letter says. They will still have solutions engineering fleet, deployed to onboaed their 'Saas product' to each client.