Yes, the original Sharknado was good enough to warrant a sequel, because Sharknado had a big following. The effects in Sharknado were compelling, and the people who like Sharnknado are very loyal. Also, sequels are not very expensive to produce anymore, so the standard to make a sequel worth it is pretty low.
Yes, this movie had a lot of fans that enjoyed watching the movie, so there was reason enough for the producers to make a second movie, which I am sure that they thought would be a lot more popular than the first. These movies were not all that bad I thought.
The original "Sharknado" was a fun, cheesy and entertaining parody of action and scary movies, but it should be left alone. It was a one time thing whose hype and originality caused it to be a success, and any sequel would not have the same energy behind it to become a success.
If "Sharknado" was good enough to earn a sequel, then why didn't they make a sequel to the 1980 campy sci-fi movie "Flash Gordon"? Both productions were cheap, campy and hardly realistic. Both movies could be seen as laughable. "Sharknado" and its success are due to an intellectually dull populace that watches too much reality television and eats super-mega buffets everyday.
Sharknado is one of those film innovations that is quirky to see one time but that has run its course once it has been done. It was unusual and oddly entertaining to see sharks flying through the air, but we now have seen it and know what will happen and don't need a sequel at all.