How does the metal can type transistor have better shielding properties? and thermal properties?
Perhaps you should investigate this. I've given you a hint, I'm *not* going to do your homework for you.
Is this the advantage over plastic package type transistors?
No, I was just joking. The real advantage is that the designers are vampires and can't stand it that they can't see their reflections in the metal cans, so black plastic causes them less mental anguish.
I didn't say it was *the* advantage. Have you thought that it isn't that one is better than the other, but that they both have advantages and disadvantages?
Have you considered cost?
plastic dual inline package IC op amps or transistors
This is neither a statement or a question.
They make Metal can IC op amps up to 10 pins
True, but not particularly relevant. I could say "they make vehicles with 4 wheels". That is true, but doesn't actually tell you much that is useful.
if you had said "I think the reasons designers pick plastic packages is because metal can packages can have a maximum of 10 pins. Am I right?", then I'd say:
If packages are only manufactured with up to a certain number of pins then saying that a designer chooses to use plastic packages for more than 10 pins is similar to saying that you choose to breathe -- you have little option.
But why would a designer choose the metal can op amps and transistors over the plastic transistor and ic op amps?
I've already answered that. There's no point in repeating the question.
If there's something you don't understand then Google it. If you still don't understand, come back and tell us what you've found out and what doesn't make sense to you.
If you think you understand, say "I think the reason X is true is because of Y. Am I right?" Then we can indicate if we think you're right or not and provide more hints if you need them.
And your question is not precise. Are you asking why designers might pick a certain package when there's a choice, or why manufacturers might choose to produce a part using one or the other (or both)? There may be some overlap here, but the flip-flopping from one to the other doesn't help.