In the 1800s, Engineer & Manager Frederick Taylor started making detailed records of how long it took employees to manufacture steel in his factory as part of an effort to improve efficiency. The amount of time it took to make steel was irrelevant to the cost of the steel – that was set by the market.
In the 1900s, more companies and industries (including legal and marketing) adopted time tracking because measuring things was cool, but also started billing with the hours logged instead of fixed fees or commissions.
And here we are doing the same thing in the 2010s without stopping and asking why often enough. What are some alternatives? Wikipedia says: