It's not. Consider the calculus: invented almost simultaneously by two brilliant mathematicians (Leibniz and Netwon).
For a more recent example, consider NP completeness, proved completely independently by Stephen Cook and Leonid Levin.
Or even reinventions made disparate by time: the Cooley-Tukey FFT was first formulated by Gauss in 1805.
If these inventions are "obvious," then all inventions are obvious. The truth, not widely acknowledged, is that most inventions are as much a product of the environment of the inventor as the inventor themselves. They're not smarter and they're not unique. Patents should not prohibit coincidental parallel invention, only reverse engineering.
For a more recent example, consider NP completeness, proved completely independently by Stephen Cook and Leonid Levin.
Or even reinventions made disparate by time: the Cooley-Tukey FFT was first formulated by Gauss in 1805.
If these inventions are "obvious," then all inventions are obvious. The truth, not widely acknowledged, is that most inventions are as much a product of the environment of the inventor as the inventor themselves. They're not smarter and they're not unique. Patents should not prohibit coincidental parallel invention, only reverse engineering.