With the current popularity of ebikes and also the availability of lower cost ebikes, the money, time & effort to convert an acoustic bicycle into an ebike are quite significant investments.
Especially when an acoustic bicycle that is not meant to handle the extra stress that comes with strapping a motor, battery &other components onto the bike, additionally the extra brake performance needed once your acoustic bike is capable of traveling at higher speeds with an electric motor.
For under $1.5k, you can get a very nice, fun, reliable ebike, complete, shipped to your door & ready to ride.
No need to spend time fussing with how to mount your motor or battery, connecting everything and go through the trial & error of setting up everything; which leaves you more time to enjoy the riding.
I've been converting acoustic bicycles into ebikes since 2014, I used to enjoy the time spent in garage testing different setups and optimizing performance; but now I just want a ebike that I hop on and ride. No longer want to fuss with stuff that could go wrong.
I ride in NYC metro where ebike delivery folks are on every block, working 24/7 in all weather, they depend on their ebikes to make a living, to be reliable and take abuse.
I don't see converted ebikes used for deliveries.
I do see plenty of cheap Chinese made ebikes among the delivery folks, lately I've seen more Lectric XP, and other fatter tire models; and I think there are good reasons for that.
Ultimately, depending on your usage of the ebike.
If you want something that you like to tinker with, spend time in garage working out the optimum performance, go DIY.
If you just want to turn key & ride, buy a complete ebike and you may just spend more time riding instead of tinkering.