Why do web podcast players never have a volume control?

I've noticed this trend with all web podcast players like overcast etc. It's annoying because I don't always want to load up itunes, or spotify etc just to listen and I often listen while I'm doing other things.

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So I find I have to lower the system volume and then raise the volume in other applications up to max if I want to be able to hear the podcast but also hear something else over the top.