Because the iGPUs aren't keeping pace, and many of the biggest/most popular titles continue to push the envelope of fidelity.
Ray tracing for example is becoming much more prevalent, and (done correctly) adds a significant amount of both immersion and overhead to the experience. It is inherently an expensive operation for GPUs, so much that most implementations rely on upscale to make it viable.
Your laptop analogy doesn't really work here; mobile chip implementations are indeed slower but can be measured as a modest percentage drop in performance to their desktop counterparts. Meanwhile, most iGPUs are orders of magnitude slower than many entry level dedicated solutions, especially for sustained performance.
Ray tracing for example is becoming much more prevalent, and (done correctly) adds a significant amount of both immersion and overhead to the experience. It is inherently an expensive operation for GPUs, so much that most implementations rely on upscale to make it viable.
Your laptop analogy doesn't really work here; mobile chip implementations are indeed slower but can be measured as a modest percentage drop in performance to their desktop counterparts. Meanwhile, most iGPUs are orders of magnitude slower than many entry level dedicated solutions, especially for sustained performance.