To all networking specialists, why would a business choose ADSL (or HSA) internet services?

You're comparing a commercial grade service with a domestic one. Domestic packages are typically an "up to" service where the available speed is shared out among a number of subscribers. As such you don't usually get the full speed, especially at peak times, and you are subject to bandwidth caps and/or throttling to ensure everyone gets their fair share of the network. The higher priced business oriented services offer guaranteed bandwidth at any time of day or night and typically no limit on how much data can be transferred. That bandwidth needs to be set aside even when you are not using it so clearly that is a much more expensive service to provide. However, it could well be far faster. A couple of years ago my employer paid to upgrade my home connectivity from "up to 24Mbps" (and around 15Mbps in practice as allowed by the line) to an 8Mbps MPLS link at around ten times the price. If may appear from the raw figures to be half to one third the speed of what it replaced, but in practice it is several times faster for most of the day.