I've been developing SPAs as an independent contractor for over 8 years, and not a single of those SPAs is public facing - they are all enterprise line-of-business apps used internally. Sometimes I wondered how employing a team of 10-15 developers to develop an SPA for 1-2years (plus maintenance) is profitable, if your targeted user audience is 2,000-3,000 internal employees of that business.

My current gig for a smaller corp (<50 employees) I am with 3 other developers (1 FE, 2 BE) and all that team has been doing for almost 1.5 years is to develop a SPA webapp that is exclusively used by the on-call phone support staff, which are no more than 4 actively working supporters at the same time. Admittedly, the business customers deal in huge amounts of money so having qualified phone support is a must here, and upselling/sales also happens on those calls.