That inflexibility of route change does have a positive side: Riders can feel reasonably certain that the streetcar line will be there for the long term. A bus line might be rerouted tomorrow. And it does happen now and then.

A streetcar line or other rail transit can have significant positive impact on real estate values, because residents, employers and retailers know that transit service will likely remain good in the foreseeable future.

A bus line has much less such effect. A BRT line might have some impact, since the investments are visible and obvious in the streetscape.

On the historical note: I agree that a major reason many streetcar systems were dismantled was because their infrastructure required significant reinvestment. The solution that seemed easiest to reach within the short term was to abandon the rails and convert to buses. Somewhere within this timeframe did transit (in the U.S.) generally pass from private operations to public. Because of the rise of auto ownership, transit operations was no longer able to make a profit for its private owners. Public transit has many other benefits, which is why local governments took on the role of operating transit systems at a monetary loss. However, many of these local agencies lacked the access to investment capital for big projects like rail replacement and upgrades. Or, they didn't see the point of doing those investments as they perceived their role as serving a shrinking segment of the public.