Some RTCs do work with a simple counter like that. This calendar nonsense is basically cargo cult from the early IBM PC days. But hardware engineers rarely talk to software engineers, and these IP blocks were designed decades ago and people don't want to touch them...

Sometimes you can get both. The full RTC is useful if want to do alarms at the first day of a month or so, but yea - those are niece cases.

Here’s a quick example that is mentioned in the rationale of the commit: hardware that is offline and powered down for a significant amount of time. At boot, without an RTC (real time clock), it will have no idea of the current date or time. Most PCs have an RTC that will keep time for a while; if the time is wrong at power up, it’s not too big of a deal to fix it. For an embedded system, though, resetting the time could be a really big deal, especially if it is headless and had no continuous internet connection.

You don't buy RTCs. You buy a big SoC with a 5000 page datasheet, of which 3-10 pages are the RTC, and you take what they give you. There is no room for the RTC type/design to be part of the part selection process for a SoC, which is why they can be vaguely crappy and nobody cares or can do anything about it.

Edit: it's a power management IC for a SoC, not the SoC itself, but you often don't get much choice of those either since SoCs tend to be designed to pair with a specific PMIC. Whether the RTC is in the SoC or PMIC (or both) depends on the design.