Imagine if you have to work with firmware an usually have to change flash chip of your router
you have to de-solder write the chip then soder it to board again, this process takes time
https://scontent-hkg3-1.xx.fbcdn.net/v/t1.0-9/14516519_1326981780659986_7595908018818790679_n.jpg?oh=9d4a43f55d3556a0e387b299fcdb60d3&oe=5866AEB4
https://www.youtube.com/watch?v=fS4Pdnn_6v0