True.
BTW, the pic you used seems to be done right: holes are drilled perpendicular to the growth direction. If you buy or build one, take care this is the case. Otherwise, fibres from the wood may damage the insects wings.
One problem with nesting opportunities is that the inhabitants need a surrounding which can feed them. While mostly more common polylectic species (feeding on a variety of plants) are attracted, event those sometimes have trouble finding proper food in settlements. Oligolectic species (specialists) feeding only one a few or even one species of plant) are most definitely not finding what they need in most neighborhoods. Surprisingly, they also don’t fly that far in search of food, if I remember correctly.
All in all, only a systemic change of our environment will have a lasting impact. But even small things count. And a small collection of kitchen herbs is a great start. They also add to your personal culinary wellbeing, by the way.