не мудрено

разг.

no wonder; it's quite simple; there's nothing strange about that

Навстречу шли люди. Никого он не знал в лицо. А раньше, бывало, не успеваешь раскланиваться. "И не мудрено, - утешил он себя. - Завод-то был кроха - чуть больше тысячи рабочих. Сейчас разросся втрое..." (В. Ерёменко, Слепой дождь) — Some people were walking towards him but he did not recognise any of them, whereas previously he could hardly manage to say hullo to everyone he met. 'But there's nothing strange about that,' he consoled himself, 'the plant was small then, scarcely more than a thousand workers. Now it's grown to thrice the size.'