Yes, you are right. There is a good reason behind that.
Referring to the Configure the priority of scheduled reports ,the main factor is CPU. Splunk Documentation states:
Splunk software determines its system-wide concurrent historical search limit through a calculation where the primary variable is the number of CPUs in the deployment. The calculation includes two parameters that are defined in "limits.conf" in the Admin Manual:
max_searches_per_cpu is the maximum number of concurrent historical searches allowed per CPU. Defaults to 1.
base_max_searches is a baseline constant to add to the maximum number of searches, computed as a multiplier of the CPUs. Defaults to 6.
The calculation is as follows:
System-wide maximum number of concurrent historical searches = (max_searches_per_cpu x number of CPUs) + base_max_searches
If your system has one CPU, you can concurrently run a maximum of 7 historical searches ((1 x 1) + 6 = 7).
Also, refer to this Impact of concurrent users and searches
Obviously you can change the limits but Caution: If you have Splunk Enterprise, do not change limits.conf settings unless you know what you are doing.
So it's always good to have a control over the number of scheduled searches running unless you have unlimited system resources and very less number of users 🙂