The 51% threshold isn't a fixed hashrate number but the marginal cost of assembling and sustaining the attack capacity. Difficulty drops hand more revenue to efficient survivors, and those operators (industrial or otherwise) also tend to sit behind better power contracts and hardware. If fees stay sub-0.5% for years, the bigger risk may be gradual centralization among the lowest-cost players rather than a sudden hash drop enabling cheap attacks.
The 51% threshold isn't a fixed hashrate number but the marginal cost of assembling and sustaining the attack capacity. Difficulty drops hand more revenue to efficient survivors, and those operators (industrial or otherwise) also tend to sit behind better power contracts and hardware. If fees stay sub-0.5% for years, the bigger risk may be gradual centralization among the lowest-cost players rather than a sudden hash drop enabling cheap attacks.