There are many reasons business owners only have a Facebook page for their business, the main reason is... you guessed it, cost.
A Facebook Business page is FREE. A free profile is great (and more so a requirement for legitimacy) if you're needing a basic platform listing with no concern for your branding. If you aspire to advertise a very stripped down version of your services and achievements to what may be a limited number of consumers, well then you've hit the jackpot.
Please, allow us to elaborate.
Pennington, Dean. "Facebook is rapidly losing millennials, US user base down 15 million since 2017." Techspot.com, 7 March, 2019, https://www.techspot.com/news/79082-facebook-rapidly-losing-millennials-us-user-base-down.html.