Why WSPR (Weak Signal Propagation Reporter) is a beacon mode, not a conversational one. Each transmission is a rigid, highly compressed message containing only callsign, 4-character grid square, and power level, sent over about 110 seconds in a 2-minute window, so there is no way to type free text. Its purpose is to test propagation paths at very low power and report spots to a database. RTTY, PSK31, and MFSK16 all send arbitrary characters as you type them, so they support real-time keyboard-to-keyboard QSOs.
Watch out PSK31 is the classic keyboard chat mode of the group, designed specifically for relaxed typed conversation at about typing speed, so it is the opposite of the right answer.
WSPR only whispers three things: call, grid, power. No typing, no QSO.