Why are most transcription factors enhancing the expression rather than repressing?
I can answer this question only based on guesses because I am not really sure about your claim that activators are higher in number than repressors. So consider this as an extended comment. 


  While activators can interact directly or indirectly with the core
  machinery of transcription through enhancer binding, repressors
  predominantly recruit co-repressor complexes leading to
  transcriptional repression by chromatin condensation of enhancer
  regions


Not really true. A repressor can simply sit on the the promoter and prevent RNAP from binding the to the latter. 


  Abstract
  
  Transcriptional repressors are usually viewed as proteins that bind to
  promoters in a way that impedes subsequent binding of RNA polymerase.
  Although this repression mechanism is found at several promoters,
  there is a growing list of repressors that inhibit transcription
  initiation in other ways. For example, several repressors allow the
  simultaneous binding of RNA polymerase to the promoter, but interfere
  with subsequent events of the initiation process, eventually
  inhibiting transcription initiation. The recent increase in the number
  of repressors for which the repression mechanism has been
  characterized in detail has shown an amazing variety of strategies to
  repress transcription initiation. It is not surprising to find that
  the repression mechanism used is usually exquisitely adapted to the
  characteristics of the promoter and of the repressor involved.




Some justification on why the number activators would be more:

A network perspective:

Lets assume an that gene-A somehow causes the repression of the gene-B. This repression can be either direct (A being a repressor of B) or indirect via some other genes. In the case of indirect regulation you just need one repressor in the network path A → B to result in repression of the latter. 

So all repressive paths would minimally require only one repressor, all other steps in the path can be activation; whereas in an activating path you would need 'n' activators for 'n' steps.

Post-transcriptional Regulation:

Now if you include post-transcriptional regulation then you can find more number of repressors: miRNAs (2588 reported in humans: miRbase-21) and many proteins as well (For an e.g. see here). Most cases of events leading to translational activation are actually derepression. It is logical in a way because an mRNA is a temporary product; it should not by default require an additional signal to start producing proteins.