For me, I get to run whatever I want instead of being limited to whatever mikrotik has implemented, eg CAKE QoS, Wireguard and dnscrypt-proxy. I also feel much more confident in the open source applications like dropbear and uhttpd than Mikrotiks proprietary implementations which have had numerous security flaws over the years.
I didn't know that open source software has no security flaws.
That’s not what GP said. Bad strawman :)
Short answer: choice, control, flexibility, and that warm, fuzzy feeling.