Lots of factors contribute.
During the '60s, 70s, and 80s teachers were not allowed to teach anything by rote, hence "tables" were out as was poetry, historical dates etc. People forget that teachers are subject to trendy whims from on high, do you seriously think that they agreed with these policies? I once heard a Head berate a supply teacher for having a class chant tables. She was his wife!
Parents have a strange attitude towards Maths, it's quite normal to hear a mother decrying her own abilty with Maths and saying her children are obviously going to be "thick", the same people are purple with apoplexy if their child's reading fell behind. How often do you hear parents comparing reading book levels? How often do they compare Maths book level?
Children are often unwilling to make an effort to learn, I used to tell them it's not measles, you don't catch it, you have to actively engage in trying to learn. So much is done for them yet hear is someone expecting them to try.
Calculators are of use only so far, I personally would not allow them in Primary school, and only in Senior schools from Year 9 when they replace the old slide rule or log tables.
One of the best feelings in life is when the penny drops for a struggling pupil and that then leads to greater confidence.