All the crew are seated in close proximity to exits -- most SLF are not and are acutely aware that once a fire starts seconds are precious.
Back in 1984, a 737 engine blew up in YYC and the takeoff was rejected.
ASN Aircraft accident Boeing 737-275 C-GQPW Calgary International Airport, AB (YYC) Reports at the time indicated that the SLF initiated that evacuation while the flight crew was deliberating. There was something like 90 seconds elapsed from taxiing off the runway when the evacuation began, by which time the windows and fuselage were melting on the fire side of the a/c and smoke was in the cabin.