Ability to have multiple projects open and copy and paste layers, comps, etc between them like exists in Pr, PS, Ai.

There must be a reason that After Effects can only have one project open at a time, but this  is the single biggest issue for me. Importing comps is messy, it often ends up importing the entire project. Every other program I use allows to copy and paste between projects within the app, and even between apps (Ae to Pr, PS, Ai, Ai to PS...) but Ae doesn’t allow this seemingly simple feature. 
Thank you.