Hows that more direct than an injection?

Probably the ease and reliability of application.

Not everyone is easy to start an IV on, especially if it's hard for them to hold still (like if they're in so much pain that they're considering between IV drugs or a suppository).

Venous drain doesn't go to the liver, first. Absorption is very regular. Works on unconscious patients.

Better that pills in every way, except convenience.

Injection is still better.

It isn’t - but if you’re a tough stick, it’s preferable to getting a central line or an IO shot.