1. Light square collapse
2. light square domination
There are two colour complexes on the board: light squares and dark squares.
In position 1 (Reti - Spielmann, 1928), black is fatally weak on the light squares.
In position 2, white is not only strong on the dark squares, but also has an advantage in space and a lead in development. After the rook swing Rb3! Black will struggle to resist a kingside attack.
A colour complex is more liable to become weak when the bishop that guards it has been exchanged. In both positions black is weak on the complex where their corresponding bishop has been traded off.
See: 'Opposite colour bishops and queens', 'Dark square strategy', and 'Light square strategy'.