I am trying to understand something. So openwrt images are supposed to fit tiny tiny images. Can't have the all the big binary drivers like the linux desktop PC's do. So we got to know which ethernet brand, which wifi. So we only and only load those modules am I right? If we had like, 8GB nand flash router, we would just flash the whole kernel with all drivers, and it would work right?
For example I got a linux installed SSD, I unplug it from my PC. Then plug it in another different PC, and it works without a hitch. This is because of all modules are already loaded in desktop linux OS's?
Yes.
Yes (or maybe).
The normal router recipes include the exact hardware definition of the hardware, so only the needed driver(s) are built into the image meant for the router's small flash.
The exception is x86 mini-pc style devices, where flash size is usually not the restriction.
Maybe maybe not. Unfortunately, with hardware, you can have some drivers that load and THINK they are for a specific hardware, attach to it, then send an initialization sequence to the hardware thart is wrong and then wedges it so the correct driver can't load.
These routers are slammed out on assembly lines a million miles a minute they are the ultimate in cost-reduced products. I doubt there's a lot of margin in them these days since so many people nowadays just use the ISP-supplied router. The primary use for them (in North America at least) is to replace the ISP-supplied router so that the user does not have to pay a monthly fee anymore for it. But, many ISP's do supply "free" modem/routers nowadays. The ISP's look at it as a way to defend against support costs since 99% of support calls into an ISP have nothing to do with service interruptions (despite what the users think)
So from the user POV if they are paying $10 a month "rent" for a ISP router, and they can buy a $120 router then after 1 year it pays them back - and people are looking at these things as "I'll probably junk it in 3 years" well that becomes a "MAYBE" kind of sell for them. So the manufacturers DON'T have a very high price point - they have to keep them in the $200-or-less range. That does NOT buy you much ram and flash - thus the cost-reduced design.
It used to be that the router vendors like Linksys, Netgear, etc. - viewed these devices as a "gateway" to leverge themselves into the Enterprise networking market. Netgear did that successfully for example, they are sort of regarded as "midrange" now, vending switches and devices suitable for a 50-300 user company while Aruba and Cisco dominate the higher end. Linksys failed because of a series of really poor ethernet switch designs. But nowadays these router divisions aren't sexy anymore - they produce steady revenue but aren't going to lead to anything bigger - and are passed around between investment houses. So they aren't going to be getting away from cost-reduced designs anytime soon.
I know right? They get poorer CPU's mostly. A 2014 high level router is probably still better than mid range 2023 routers.