You still bought a job, not a business. Your job is manager instead of driver at best. At it's most common, being an ISP or whatever today's term is, you might work part-time for minimal return on the total investment. At worst, you are still a driver, a part-time mechanic, a service scheduler, HR manager, etc.
Most of the ISP 'owners' claim a maybe 12% return on investment, but conveniently forget to pay themselves for the hours they put in. ROI is calculated after payment for all expenses including your own labor at market rate. Anything else is just lying to yourself to justify being in this 'business.'
If you are grossing $100k on a $400k purchase, but working 40 hours a week managing the enterprise, you aren't getting a 25% ROI. Managing 5-10 people(or more) working with payroll, working to maintain vehicles, even overseeing managers are all part of a job that would pay about $75k a year or more. Then you have the cost of money- what your investment could otherwise earn passively. Just simply investing in the stock market nets about 8%, and real estate is about the same. Earning $25k from the investment is around a 6% ROI.
Someone could easily take the same $400k, get a job with benefits maybe at UPS, invest the money, and come out ahead- except for the unskilled, who tend to be the supporters of this model.