What do YOU play after 1...d6? Most of the times Black will go 2...e5, but this is not the only option.
2.e4 c5 is a Sicilian, most of the times not wanted by Reti players, 2.g3 e5 (or pretty much any reasonable move) is hardly conclusive or anything, and 2.d4 Bg4 is a fairly respected "white square strategy" positional approach (Black wants to go on like ...e6, maybe also ...c6 and d5 etc).
And against 2.c4:
What do YOU play after 1...d6? Most of the times Black will go 2...e5, but this is not the only option.
2.e4 c5 is a Sicilian, most of the times not wanted by Reti players, 2.g3 e5 (or pretty much any reasonable move) is hardly conclusive or anything, and 2.d4 Bg4 is a fairly respected "white square strategy" positional approach (Black wants to go on like ...e6, maybe also ...c6 and d5 etc).