Adding to your list....
Salt Lake, Garfield and Western with service between the west side of Salt Lake City and Saltair Pavilion located maybe 15-miles (?) west of town.
Aurora, Elgin, and Fox River Electric which went from overhead trolley wire to diesel (from the I.C. connection at Coleman, Ill to the Illinois State Hospital in South Elgin, Ill.), but this line is electrified (if somewhat truncated) today as the Fox River Trolley Museum.
Woodstock & Sycamore (I'm not sure if I have the complete name here). This northern Illinois line had big plans to electrify, but the closest they came to that goal was a petroleum-fueled McKeen car or two.
The Milwaukee Electric with service to one of the Wisconsin Electric power plants south of Milwaukee, but very close to Lake Michigan. Trolley wire and steeple cabs powered this line for awhile after the TM gave up passenger service, but I think it may have gone diesel afterwards.
Yakima Valley Transportation in southeastern Washington State.
Might the Washington, Baltimore & Annapolis qualify?
Nothing is more fairly distributed than common sense: no one thinks he needs more of it than he already has.
You can add the Lackawanna and Wyoming Valley (Laural Line) to the list. They also ran diesel freight after ending the electrification which followed abandonment of a good passenger service with hourly service and two-car trains during rush hours. Part of the line has been restored and re-electrified as part of the Electric City (Scranton) Musuem operation which does serve a transportation need in transporting people from downtown Scranton to the local baseball field and which includes a tunnel. The Laural Line was mostly third rail, with the exceptions being the Willsbarre end and the single-track South Scranton branch, but the museum operation is conventional trolley wire. The car in use is a double-end heavy center-door car from Philadlephia Suburban - Red Arrow converted from wide to standard gauge. Its right by Steamtown.
The interurban cars used by Laural Line were steel mu cars much like those on any electrified suburban railroad, but with trolley poles, not pantographs, as well as the third rail shoes. There was a loop at each, so the cars were setup for single-end operation, but with backup trolley poles. Color was closed to Pennsy Tuscan red, but if my memory is correct, white lettering. It was a fast operation. When I rode it several times, there were still four local trolley lines operating in Scranton, Nay Aug Park, South Scranton, Green Ridge Peoples and Green Ridge Suburban, and the Nanicoke trolley line still ran south from Willksbarre with a branch and shuttle car to Hanover, the junction being close to San Souci amusement park. Scranton had ten of the somewhat modern looking Osgood Bradley "automotive" design lightweight cars, similar to Brill "Master Units", and the rest of the cars, and those in Willksbarre, were regular-looking double-truck lightwieghts. Blue with white trim and lettering in Scranton, and brown with red and white trip in Willksbarre.
Can't help you immediately on the "why" question for BRR, but the BRR RS1 was around when electrified freight and passenger service was still running (summer of 1950). There are some other examples similar to this, CCW had a non-electric (can't immediately recall if it was a diesel- or gas-electric) switcher on the property at the same time that it was still running electric-hauled freight service.
In the realm of other electrified carriers that dieselized, there's also Salt Lake Garfield & Western (can't recall if this was on your original list, or not).
Have you seen this book-
Hilton, George W. & Due, John F. (1960, 2000). The Electric Interurban Railways in America. Stanford, California: Stanford University Press. ISBN 0-8047-4014-3.
You may be able to get it through an Interlibrary loan.
Some additions:
Bamberger,
Des Moines & Central Iowa,
Sacramento Northern,
Central California Traction,
Tidewater Southern,
Visalia Electric,
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