Above the weather
Almost all cloud and storm activity stays below the tropopause. Platforms at 20 km fly in clear, stable air with an unbroken view of the ground.
On station for days
Satellites pass overhead in minutes and aircraft head home in hours. A stratospheric platform can hold over one area for days, giving continuous coverage rather than snapshots.
Hundreds of kilometers of reach
From 20 km the horizon is roughly 500 km away, so a single platform can observe, or relay across, a region hundreds of kilometers wide.
Recoverable and reusable
Launch on demand, bring the platform down for maintenance or a new payload, and send it back up. No launch windows, no orbital mechanics.