It is easy to purchase seeds from online websites, many of these seeds do not germinate and the time, money of the person who purchased the seeds is wasted. For example for the last few years, the domain investor has been trying very hard to grow karela plants.
A few decades ago, the karela plants were growing very well, without any kind of fertilizer or special attention. However it is observed that due to high radiation levels or similar problems, not a single karela plant has grown in the last few years despite trying at many different locations.
So though seedlings are expensive, it is worth purchasing them instead of wasting time and money trying to grow plants from seeds.