MLFLE does provide a thorough explanation. From the time MLFLE introduces the number 10 (in level 1) it explains place value thoroughly, that the number 23 is 2 groups of ten and 3 ones. MLFLE then takes that strong knowledge of place value and shows why we borrow and carry (starting in level 2, I believe). MLFLE has shown us the relationship between multiplication, division, and fractions (in level 3). I know, at first glance, people may think the pages look too simple, but I love how MLFLE teaches why we solve problems in a certain way and not just how we solve problems in a certain way.
ETA: The lessons are short but not to the point of being ineffective. There are hands on activities.
ETA2: Other concepts are being taught in those levels, not just place value, double digit addition/subtraction, multiplication.