The issue is less that it's impossible to make time for something like that, the issue is that
a) you aren't as firmly in control of your day, so planning that sort of thing is just one overflowing diaper away from not coming to fruition.
b) there are a lot of little things like this to be done throughout the day. From sterilizing pacifiers to preparing snacks to recharging the baby monitor, running the washing mashine again because someone has drooled carrot-puree all over their socks again and you don't even know how it got on nothing besides the darn socks, but in the end, you are officially out of fucking socks now and need to wash some, etc. Those add up rather quickly.
While each of them can be seen as "not a big deal", one needs to consider that the parent doing all of those little things has a child that will demand attention in uncontrollable intervals for uncontrollable reasons, so things can take way longer than they should (It took me well over an hour to type this because my son has trouble staying asleep today).
So, since only so many todo-list-items can get done in a day and parents have the same 24 hour day as the rest of earth, parents usually find themselves in a situation where they can't do all the things they want to do for their child. So having those products instead of homemade stuff is usually just a result of parents not being able to prepare enough homemade things by the time they are needed. So they do something else for their child and buy those packages instead. This is ignoring that children can have pretty peculiar tastes and might just not eat fresh fruit for no reason at all or eat only the bought stuff, no matter how similar the homemade tastes.
Sorry for the long and rambly answer, I'm too tired for a shorter one. I hope I could somewhat convey why many parents see it as ignorant when non-parents just tell them "yeah, you just need to do this additional thing, you are not an ideal parent otherwise and worthy of judgement. This one thing is really not a large thing, so just do it, alright?" while blissfully ignorant as to why doing just "one little thing more" might actually not be in the parent's or even the child's interest. I'd rather have a child eat those packs and have a parent with just that little more time to actually be with the child than the other way around.