If you're flashing firmware and it is interrupted the firmware will be unusable. The computer cannot boot without viable firmware. You'd need a 2nd backup firmware to switch to, but that would complicate things and cost more money. Also you wouldn't ever want to create a system that could leave some users running computers permanently switched to the unflashable protected backup firmware that has critical bugs in it that leaves the computer vulnerable to malware. So there's that to consider as well.
Best to consider firmware flashings something that must not be interrupted under any circumstance, ever. One advantage of being a laptop over a desktop computer is the built-in battery, so power loss is much less likely to be a cause of failed firmware flashings...