Why is fiberglass antenna not suitable for indoor use? What environment is suitable for application?

In the construction of walkie talkie wireless systems, omnidirectional fiberglass antennas are used as relay station antennas. Is the gain or length of the fiberglass antenna better? What are the characteristics of fiberglass omnidirectional antennas in detail, and can they be used as indoor antennas? It is estimated that non professionals cannot provide detailed answers. Today, the editor will talk to you about omnidirectional fiberglass antennas:
Why fiberglass antennas are not suitable for indoor use
Many people may notice that international brands such as Linksys or DLink typically only use 7dB, 5dB, or 2dB antennas on their devices, but rarely see their 9dB or higher gain indoor omnidirectional antennas on the market. Based on our general understanding, 7dB antennas have fully met the requirements for indoor use. Antennas with 7dB or higher may have the opposite effect due to their smaller angles and inability to exert their advantages. Therefore, omnidirectional antennas with a bandwidth of over 9dB are definitely recommended for outdoor use. As for some people who say that indoor use has good wall penetration effects, this statement cannot be verified, so there is no need to be overly confident.
Why is it called an omnidirectional antenna, and there is also the theory of vertical angle
The omnidirectional antenna commonly referred to in the construction of wireless antenna systems refers to an antenna with a degree radiation angle of 360 degrees, which emits in a fan-shaped manner vertically. The angle is usually around 6-15 degrees, and the higher the gain, the smaller the vertical angle. For example, a 9dB antenna can achieve a radiation angle of about 14 degrees, while a fiberglass antenna can only transmit signals at around 8 degrees, which was once the limit. Due to the small vertical angle, it can only transmit signals at a degree of 6-8 degrees. Therefore, fiberglass antennas are commonly used for wireless masking in plain areas, as well as in the same degree position environment, and in the same degree position environment. If mounted at a higher position, signals can only be transmitted to distant areas. The position cannot be concealed by the nearby or central areas with height differences.