It is cost prohibitive to buy a strut unit and buy OEM springs and top mounts and really there is a limit when working on a customer car vs doing job on your own car. We have never had a problem with a strut assembly having lower quality springs or the strut tops so that is the route we take.
Theres also the reality of parts availability. If you can order online, ahead of time, you can build them. I've got a snapped coil spring and a bay *******, neither I nor the vehicle owner I have time to wait a week for OE springs from a local dealer, let alone bump stops and similar small bits.
I just waited 10 business days for a fuel line assembly for a mid 2000s dodge truck. For most people and shops, that isnt a sustainable business model.
The beauty of DIY is one of two paths. Absolute bottom dollar running costs, use the cheapest stuff you can get by with and minimize total cost. The other is use shop repair costs as your price ceiling and use awesome/premium parts and save cash because the labor is free. Even after buying tools you can still be ahead and potentially do a superior job with better parts. If you enjoy the process and the tools? You're almost making money at that point.
FWIW Honda will sell you a prebuilt OE strut assembly with all honda parts.