It’s mostly the plugins!
The real question to ask is why do plugins take so long to open and there are numerous reasons
- Physical loading of plugin code into RAM - that’s mostly just for the first one - subsequent instances of the same plugin share the same code so code doesn’t have to be physically reloaded
- Plugin initialization — can be arbitrary depending on what the plugin wants to do. For example, if a plugin wants to connect to its home server, even if just for an update check and you don’t have an internet connection, if not properly implemented, a plugin might wait a significant number of seconds waiting for an IP address to be resolved
- Licensing - some plugins do really funky stuff for licensing that might take multiple seconds
- Sample loading - if a plugin is loading samples into RAM, it might not be asynchronous and you have to wait.