That's not the key phrase, except to you perhaps.

I'm supposing the tax is only paid when a business is actually paying wages...employing people...and there are quite a number of businesses who do not have employees all year, or have no employees at some parts of the year, or a seasonal surge of employees. That's why the "when" of payment calculations is important...or a more thorough explanation of how this tax is collected.

In terms of bias, yours are usually obvious and predictable, but I am biased against employers who cheat employees, and we're seeing it reported in news fairly often.