The problem with integrating time tracking with other business systems is that outside of software development the tools utterly suck for integrations. Integrating with calendaring apps or task management or CRM is either really hard because there isn't a public API or the tools are very basic because the API has to easy to use, or the system is expensive to develop for being the API is complex. Plus the API ends up dictating how you organise the data rather than the business choosing how to use the tool - eg 'every job must be part of a project that's owned by a client' .. that sort of limitation quickly makes the tool inflexible and hard to use.

If you look at integrating with software development tools like ticketing or bug tracking you have to remember that in the majority of companies, even if you only look at software companies, most people aren't developers once you get to more than about 10 staff. You have sales and admin and managers. What that means is that you either end up with a time tracking tool that does very little outside of tracking time or a time tracking tool with a raft of features that don't apply to most of the people using it. Both of which are bad for some of the users.

All of this is compounded by the fact that most people don't want their time to be tracked. Even if you love your job, having someone reviewing how you spent your time feels like you're being micromanaged and watched over. That just isn't a good feeling.

Time tracking is a surprisingly hard problem to solve once you get past just a log of 'On A/B/C worker X worked on Y for Z hours'.