You get what you pay for
As has been noted (Will Godfrey) there are better cabled systems that have sophisticated detection mechanisms that alert when it thinks it's being interfered with. But these systems cost lots of money. Even excluding the cost of the actual devices, there's the cost of running cable, which is often the most expensive part. Sure, lots of us who read this site would probably run the cables ourselves, thus saving bucketloads of money. But 99% of the people out there who get a security system would hire someone to do it for them.
So, the alternative to spending a couple grand on getting cables run all over the place is wireless. The people who are installing wireless security, which is much easier to do and hence can be done by more people (as opposed to hiring someone to install it), are already looking to save a buck. Therefore a lot of wireless kit is aimed at these DIYers, but not DIYer enough to go running cable through walls.
And the people who want a bit of security but who don't want to spend much money on it are people who are looking to deter minor criminals. Opportunistic criminals who are looking for a quick and easy buck. They wander the streets looking for premises that have no security, are unlocked so they don't even have to break a window or pick a lock. All locked up? move onto the next house. ANY signs of security, don't even bother looking for unlocked access, move onto the next place right away. This is the profile of over 95% of house burglaries. Your junkies looking for a quick fix, loose cash or some DVDs they can sell at a used DVD store or similar, nothing complicated. Nothing that requires fences (as in people who dispose of stolen goods) and so on. This is the level of security that the wireless security systems are aimed at.
Then you have a higher level of crims. The ones who actually pick targets based on other criteria. Affluence, types of goods they can steal and so on. These guys are going to have jammers, and be able to defeat the cheaper security systems. But these account for a tiny % of breakins. If you have enough valuables to think that you might actually be targeted, then you've probably got the money to spend on a higher grade of security system. The sort that makes these higher level crims decide to move on to easier pickings.
Then you have a nigher level above this, businesses or people who will actively be targets. Pharmacies, shops that have a lot of cash on-hand, rich people, people doing the dodgy and might come under investigation from the police (i.e. crims themselves, drug dealers and whatnot). So they ratchet up security on these locations. Everything cabled, back-to-base security (maybe not for the drug dealers ;) ), panic-button alarms and so on. More likely to be specifically targeted, better, more expensive security.
Then there is a category above this, banks, diamond merchants, even better security systems to the extent that they may have onsite security guards/teams. And this is without even considering military/national security/industrial espionage and so on.
Furthermore, the point of security is not to a 100% (or even 10%) guarantee no-one can break in. It's to make it harder, such that there are easier pickings out there. You have a crap home with not much in it, but put up a couple cheap-arse, low-quality wifi cameras, and the junkie after enough money for a hit is going to break into the next door neighbours house who doesn't have any cameras.
If you're a fat rich bastard who has a house that's got an art wing, a theatre, a vault, a panic room, a garage with rare cars, then you are going to spend hundreds of thousands on a security system that has random security drive-bys, back-to-base alarm with motion and heat sensors.
You decide what category you are (no-one with nothing special, got a bit of stuff, got something significant worth protecting etc), and the type of crim you want to dissuade, and the amount of money you want to spend, and buy the security system that intersects as much of those needs as possible.
Biting the hand that feeds IT
