Shuttle buses (24-28 occupants) do quite well on twisty suburban roads. Those same roads often have curbside parking, and delimiting a 30-foot stretch of road as a bus stop is not going to seriously hamper that.
I'm not saying LA should be this way, it just is this way. The suburban sprawl makes most of Southern California a shit show for public transit. Cities with effective public transit tend to have higher population densities at least more concentrated commercial areas. In SoCal (tired of typing it out) places where jobs are located are distributed all throughout the sprawl. There's no real "downtown" where all the jobs are located.
It also doesn't help that due to earthquake and fire codes it's rare to see mixed zoning in much of California. So few neighborhoods with ground floor commercial/retail and upper floor residential zoning.
In Vancouver, the cost to operate regular buses, per revenue-hour (time the bus is carrying passengers) is ~$120/hour. The cost of operating shuttle buses is ~$70/hour. [1] This is because smaller buses use less gas, are cheaper to maintain, and have better labour utilization (Time the driver spends on the clock driving passengers, versus time the driver spends on the clock waiting around, switching routes, etc.)
And this is operational costs. Capital costs are another huge factor, that's not accounted for in the operational numbers. It costs a lot more to order an 80-passenger bus (And even more so for a trolley), then it does a 24-passenger one.
Also, this is only anecdotal, from being a rider, but I'm pretty sure that shuttle-buses both perform better in congested environments, and cause less traffic congestion (As they have a much better power-to-weight ratio, better acceleration and breaking, a smaller turning radius...)
[1] https://www.translink.ca/-/media/Documents/about_translink/g...
The capital costs of the bus isn't that much different over the lifespan of a bus. If you need a large bus at all, then it is cheaper to buy one large bus than both the large and small. Small buses cost less mostly because the drivers don't have to be as well trained - I'm not sure I want that difference.
This worked because shuttlebus service was slowly ramped up year over year.
The small buses are solely used for last mile suburban routes, the large buses for anything else.
Once in LA itself the buses have the same problem of not being able to really drive on the smaller side streets so they're limited to the big avenues. That makes them slightly better than LA's trains but still a pain for a majority of riders. LA doesn't have the space in most places for dedicated bus lanes with above-grade platforms.
Note that LA has lots of bus lines but commuting on them is tedious and slow. Getting where you need to go usually requires several transfers then travel on foot to your actual destination. For most commutes it takes at least as long as driving.