Well people have already given many reasons... I'm not sure if this will be valid anymore but here goes.
The best reason I can think of to continue would be that all the routes are their own genre of a story so even if you end up hating the rest at least one or two will possibly appeal to you based off of preferred genres. If I had to give the common route a statement of purpose with the rest of the novel I would say that it is a basis of comparison in contrast of tone.
If you want a more personal reason why I think you should continue is that I loved the themes presented. Instead of family or friends like Clannad and LB! respectively, the theme presented is something like humanity or life. This leads to a different form of overall impact and gave birth to what I think is one of the best endings I have read. It is one of the more philosophical stories I have read and it is overall a lot bigger than it seems. The quotes are very meaningful and can be used.
There are more things to say but a lot of the reasons I enjoyed it is irrelevant here or you should already know from the start of the thing but I hope this helps in some way.