The illusion here is that simple/less complex apps are better. But the reality is that more simple apps with fewer features means the end user needs more apps to manage their business or their lives.
Your invoicing app may be simple and let you send an invoice, but does it integrate with your time entry system? Wouldn't a time entry system that does invoicing or an invoicing system that also does time entry be better than two disparate apps that do one or the other? Who wants to waste time entering the same information twice? Making data entry mistakes? Flipping between different apps, usernames, passwords...
The problem with the simple is better line of thinking is that it actually complicates the business life. Multiple accounts at multiple sites. Multiple payments to multiple vendors. Different user interfaces to learn at each site. Different ways of doing things. Maybe the enter key over there submits the form, but it goes to another field somewhere else.
All these separate systems are really just features of a business management suite and I'd rather keep all my stuff in one place than have 15 accounts at different locations to do one thing. If I can pay $50 a month for a system I can customize to do what all these 15 sites do for $10-99/mo I'd be a much happier customer.