If tech gets "smaller" over time (today's phones still being pocketable with 10x more power than before) why have handheld game systems got bigger?

In 2004 during the PS2 era Sony made the PSP which could fit in your pocket and had near console graphics. Now with the Switch and these handheld PC devices, they are tablet sized and none of them can handle current graphics at reasonable battery life vs what the PSP did. Why is this the case now?

If tech gets "smaller" over time (today's phones still being pocketable with 10x more power than before) why have handheld game systems got bigger?
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