Why does the reactor production path for transuranium elements end at fermium-257?

The production of transuranium elements in nuclear reactors via successive neutron capture terminates at fermium-257 because of the extreme instability of the subsequent isotope, fermium-258.1

Specifically, the production path is limited by the radioactive decay characteristics of the next isotope in the sequence. Fermium-258 undergoes spontaneous fission with a very short half-life of approximately 370 microseconds. This rapid decay effectively precludes the accumulation of fermium-258 and prevents the synthesis of isotopes of elements with higher atomic numbers through this specific reactor-based process. While spontaneous fission is a general phenomenon, it becomes the dominant mode of decay and a limiting factor for the heaviest known nuclides, as the probability of this process increases dramatically as nuclei become heavier.12