@AliEmirSisman
It may be that the service area travel time/distance breaks you are using are too low for that particular location.
Do you get this error warning: "030247: One or more break values could not be reached by one or more facilities."? If so here's the accompanying text in the documentation:
When solving a Service Area network analysis, sometimes the specified break value, or cutoff, cannot be reached from a facility. For example, you may see this message if you specify a break of five minutes, but it is only possible to travel two minutes from the facility. In this case, the resulting service area represents the area reachable from zero to two minutes from the facility instead of zero to five minutes. Possible causes include the following:
- Network restrictions, U-turn policies, or barriers prevent travel along roads providing access to the facility.
- A break value so large that the entire network dataset can be traversed without exceeding the break.
The fact you are getting small service area much just be because of the real-world characteristics of the location and its connectedness to the network data you are using.
I recently ran a similar analysis and was surprised by an odd result like this - the reason was that the location in question had no pedestrian access to the rest of the network as it was a motorway service station.
Hope that's a help
