Shutting down part of the system

BART has had two major unplanned service stoppages in the past few weeks, both caused by fires. The first one was between Pleasant Hill and Walnut Creek, and the second near Fruitvale. In each case, in addition to stopping service at/between the affected stations, they also stopped service to adjacent stations (no service between Lafayette and Concord, or Lake Merritt and San Leandro). My question is simple: Why?

I want to be clear: I'm not bashing BART here. I assume they had a good reason to stop service where they did, I just don't know what it is. In the Pleasant Hill incident, it looks like there are sufficient crossovers to turn the Pittsburgh / Bay Point trains around at Walnut Creek, and the SFO trains at Pleasant Hill. I didn't look as closely at the track configuration on the Fremont line, but I'd be surprised if the lack of crossovers was the only reason they set the size of the shutdown how they did. What other factors come into play here? Can the third rail power not be shut off in small enough segments? Is there something about the crossovers that I'm missing? Passenger capacity issues? (I call bullshit on that one for the Pleasant Hill incident; Lafayette was in total gridlock)

Plain and simple, central would rather play it safe and keep trains away from an incident rather than trying to single track or bring trains too close to an incident.

Train service stopped at Lafayette because the incident train that ran over the power line was at Walnut Creek and they needed to keep power off at Walnut Creek to remove the power line that was tangled under the lead car. I don't know off the top of my head, but the third rail section where the power line fell in probably extends to Pleasant Hill, and even if it doesn't the crews responding would still request it to be powered down because of the proximity to the power line.

I don't know what exactly happened yesterday, just that the train stopped near A25 interlocking between Fruitvale and Coliseum with a report of fire, which may have been caused by electrical arcing. At one point there was a report of a group of 2-3 passengers that broke windows/doors in the trail car and jumped out of the train. The operator walked though the train and moved all passengers to the lead (origin of the smoke was the trail car), and the train was eventually moved to Fruitvale where passengers received medical attention.

Third rail sections can be very long, so it wouldn't be surprising if that had some effect on service, or possibly third rail power was shut down in more than one area to be safe. Again all the public really has now is speculation, I'm sure we will know more facts later on.

TL;DR Just because there are crossovers it doesn't mean it is safe/possible to turn back trains closer to an incident.