People (1) don't do their own arithmetic/analysis, and (2) they believe the bank ads.
Re (1). if you don't know how much of your spending is temporary (i.e. children, paying off a mortgage) and how much is spending that will still happen in retirement (food, house maintenance and municipal taxes, clothes, vacations, etc.) then you don't have a clue as to how much retirement income you will need. And other costs - for example, if you have group health insurance at work, can you continue to get group health insurance when you retire? I do, my union has a group plan for retirees. If it didn't, I could have decent health insurance through my alumni associations or through Costco.
Re (2), anyone with a pension coming needs to know projected pension income - I don't need $1.5 million in investments (like the banks say I do) because I have a defined benefit pension (main income), a defined contribution pension (much smaller becasue of many fewer years of contribution), my CPP and my OAS, plus RRIF income (not huge, never had a lot of RRSP room because of the work pensions) and other investments (small). If we look at the cost of annuities that would give the same income as my pensions and CPP, I probably do have the equivalent of $1 million, but I sure don't have anything even close to $1 in investments.
Of course if you retire and continue to give your children huge amounts of money (house down payments?!?) or massively overspend, or never bothered to take advantage of company pensions or RRSPs or TFSAs, and you had the income to do so, then your retirement planning definitely is in trouble. I am not talking low-income earners here, they will probably have as much coming in through CPP and OAS and GIS as they did when working, and there are all sorts of low-income credits for them as well. They won't be rich, but they won't be destitute either.
The above is like preaching to the choir here, but let's face it, most people think their personal finances are too complicated to cope with, and leave it to others. I'm a retired biologist, not a financial planner, but when I go in to visit my financial contact at my bank, I know as much about my goals and possible methods to reach them as he does, and I always go with a list of topics to be discussed (which tend to match his). He is always surprised at my level of preparation, so I gather most of his clients are not doing their homework.