They pretend it’s because the women are immodest, but in a Moslem country, any woman out in public without bodyguards is likely to be insulted, grabbed and groped, even in full Islamic swathing.
Mainly true (the "no-go" areas). Those outnumber the "go areas" where women in full Islamic garb can walk alone. Generally they will go in small groups, but don't require men along. That includes most markets, malls, etc.