For those interested: these steps above could actually be replaced with just “turn the phone on while holding volume-up button and plug usb cable in”, so you can try that first before doing the battery dance - however, the phone itself gives no indication that you actually succeeded and there may be some edge cases where it’s not so simple, so the official steps are slightly complicated to make the instructions more bullet-proof (at cost of being a bit annoying)
(just clarifying since I’ve seen people in the past asking about why is taking the battery out necessary 
)