The funny thing is that our Solar System may in fact be quite average. The problem lies in being able to detect exoplanets at all. The larger and closer a planet is to a star the more likely we are to detect either the wobble of the parent star or change in brightness from the transiting planet. In both cases, being close to the star makes it more likely to be detected since the orbital period is short. It also helps if the planet is large and massive such as gas giants which are really the only ones that can affect a detectable wobble. The larger surface area of gas giants also makes the change in brightness caused by a transit large enough to be detected. Our Sun’s planets, in contrast, would be hard to detect. Jupiter’s period is about 12 years which means it would take that long to see a wooble cause by it and be able cancel out the Sun’s proper motion. It is also how long you would need to wait (assuming the observer’s line of sight aligns with our ecliptic plane) for anyone to notice a repeat of the begining or end of Jupiter’s transit. Saturn would be even worse for detecting a transit since its period is 29 yrs. A Uranus or Neptune transit may be seen only once in a lifetime if at all within either period of 84 yrs and 165 yrs. Smaller planets, because of their proximity to the Sun like Mercury, Venus, Earth, and Mars would transit more often but would be harder to detect. So, it should not be surprising that the vast mayority of the exoplanets detected are Jupiter size.
There is a size comparison of all the planets to the Sun (notice the four large gas giants) in the simulated image below: