The only reason is that this is the default setting from a filesystem which was developed more than 15 years ago at a time spinning hard disks were still the standard and SSDs hadn’t yet hit the consumer market.
It’s quite easy: Best is to avoid any “re”-branding and only buy your products from brands that are flash manufactures - I think there is about 3 or 4 companies left in the whole world.
If you want to run your operating system from sd card you want a high i/o performance which is not in par with advertised high read/write speeds as they always measurement for sequential read/writes 
So for example the “Samsung pro endurance” card which @zagnuts used is the wrong kind for a operating system. It claims “high speeds” but that is only true for continuous writing large chunks (like videos or images for example) on the other hand this card doesn’t even mention the i/o performance. 
The go-to cards are ether A1 or even better A2 rated cards for the intention of running a OS on it:
Application Performance Class | SD Association
Still - if the card is rated A1/2 or not the write amplification with a 5 second commit interval will kill it much faster than necessary 
Just as an idea what is possible with the “right” filesystem settings: I’m using some SBC’s with armbian (which comes with correct settings to don’t kill the flash) and they run on cheap (sub $10) 8/16GB SD cards (A1 rated) that are up to 
years old. Yes, running 24-7 on the first card I installed it - I expect it to continue to run for another decade or two. It might even that the sd card will survive the SBC (that probably degrades faster because of the produced heat).
Yes, A1/A2 cards are “only” about performance not about life expectancy if someone kills the valuable flash cells by flushing a page every 5 seconds 
No, this setting is not about performance but only to get the minimum wear out (maximum life time) out of flash storage. The commit/flush interval is actually the maximum time to wait for a write to the physical storage. So the system essential waits a maximum of the configured time (default 5 seconds) before it writes to flash (the minimum possible for flash is one page).
If instead of the default - a interval of e.g. 600 seconds is chosen the system will accumulate all data that is “ready” to write to the flash till it is enough for a full page write (that’s the optimum because no extra wear on the flash) or till the “time” is up - in that case it writes to flash after 10 minutes even when there is not yet enough data (typically 8 or 16kb) for a whole page.
The reason this is the default was that hard drives can allocate each and every bit so they don’t suffer from write amplification at all.
But one thing is to keep in mind: A potential power failure can cause data loss up to the configured interval. So if the system keeps the data which should be written to the storage for 599 seconds in RAM and wants to write it in the next second but the power fails all that data from the last 10 minutes is lost. 
That said it is a very minor problem - instead of buying a sd card every year or spending a fortune on “industrial grade” sd cards one can just invest a few bucks in a power bank which can be charged and discharged at the same time 
aka poor mans ups 