You asked why not web only. I said people don't want to give companies or other people their data. Using an online web tracker is handing your data to someone. Some people don't like giving their data over when it is not necessary.
I would always opt to run software on my own computer rather than on a web based solution. As someone that sells software and services with varying different payment and platform options I can see it from both sides. Both online and offline have their pros and cons.
Online software tends to cost more over time and you have less control, generally.
