In genuine science, no one argues that a lack of alternative explanations is by itself a sufficient reason to consider their theories correct and accurate. In pseudoscience, such arguments are made all of the time. In logic, this is commonly referred to as an argument from ignorance: something is claimed to be true merely because it hasnt been proven false and/or no alternatives have been proven true.
Properly performed, science always acknowledges that the current failure to find alternatives does not indicate that a theory in question is actually true. At most, this theory should only be regarded as the best available explanation something should be discarded if and when research provides a better theory. This is because science is supposed to be driven by the data rather than by the theories.
Granted, scientists are human beings and they develop personal attachments to their favorite theories. It is also true that the ways in which theories structure our perspectives will have a significant influence on how we perceive the data in the world around us. Ideally, though, data should be primary and the theories used to explain why we have the data.
Facts about the universe are the fundamental units of what science works with. Whether we decide to change our explanations or keep our explanations on how the universe work, it should be done because the facts require it rather than because our pet theories make it more convenient.
In parapsychology, however, arguments from ignorance are raised to an art form and constitute the basis for the entire field. The so-called psychic powers that parapsychologists claim to study are defined in an unusually negative manner. The aim of experiments is not to find data which the theory can explain. Instead, the aim of experiments is to find data which cannot be explained. The conclusion is then drawn that, in the absence of any traditional scientific explanation for some particular result, experimenters have come across evidence of something paranormal or parapsychological.
Part of the reason behind this may be that parapsychologists do not appear inclined to investigate the causes of supposedly psychic phenomena. They certainly spend a lot of time trying to show that such phenomena do occur but as to why they occur, well, we hear nothing at all. This is strange because a theoretical framework explaining why they occur would help point to when they would occur and this, in turn, would be a great aid in developing reliable experiments to test. Thus, the lack of such a framework and relevant explanations is fundamentally self-defeating.