Please explain why some Insert Media have image sizes and others don’t

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Hi, I’m fairly new to WordPress and noticed that depending on the Plugin, when I insert an image sometimes it has the ability to choose one of the other sizes and sometimes not.

Insert Media into a Post (see bottom right – has size picker)

Insert an Image into a Slider (3rd party plugin) – does NOT have the size picker?

Reason is that the slider uses the FULL image size which is huge and affects page speed.

How can I get the size picker?