reason for this, to me, is partially induced by the amount of work/materials required in a company to get the job done.
When you start it is really close to what you do in your house, so you go to the mall and buy a router, a laptop and so... you do not think about planning, it is just another piece of HW you need, like the smartphone. You do not hire a consultant to buy a smartphone.
a SMB with no more then 10 people will need not so much, maybe just an intervention now or then, let say to change a burned router every 3/5 years, or a broken disk in a NAS. This stuff is so rare that the SMB do not hire competent people to manage it - they just buy stuff like in their own house-, therefore, the SMB has a relevant degree of ignorance on a topic.
the commercial guy in front of the SMB is (apparently) a huge source of information for the SMB, they do not need to go deeper on tech details: they can't even totally understand what the commercial is exposing.
Now you will say: hay, consultants are there for this very topic: let SMB not be fooled/deviated by bad commercial practices.
Yes, but this implies that the SMB has - at least - a bare minimum degree of knowledge about its own ignorance.
Unfortunately they have not. Everything starts with something small, let say a small 2-disk NAS. Hey it worked! now what, oh we need a small server. Hey the commercial guy has solved the problem last time, let's call him again, he will solve it!
Then you start buy stuff and stuff, in the end IT is not the core business it is just like other tools you need to make the job done. period. what matterst is if you have margins.
Here is where you start thinking about consultats. when margins are hard. and the bigger you are the harder to keep margins high. therefore you start minding about what you are doing. And consultants start here. But it is not the IT consultant. the IT consultant is at the end of the queue, first you start with company organization, with people and procedures, THEN you ask for consultancy on tools.