First --- There is cost
1. Cost of the infrastructure to support the amount of expected traffic
2. Filtering software / Hardware to make sure everyone is safe on the network and nothing illegal is going on so the company is protected from liability
3. Maintenance costs
If your work has 10Mb internet connection that would have to be share with everyone and in order for it to function with anything more than 10 users you need good QoS hardware. As well you need AP management Hardware and software. WLAN controllers are $1500 a pop not counting the cisco router that it goes in. Then you have to consider site surveys and power consumption as well as routing and POE equipment. THEN there are VLANS to setup......its not a simple matter unless you work in a small office or small business like say a rest home.