What happens if your opponents never let you win the bid?
I will expand on Benjamin Cosman's answer by noting that:


The behaviour you are observing is bad bridge; and
The (scoring) line in Rubber Bridge is simply that, and a means (other than a time limit) for ending the match. The winner is determined by the total of points obtained both below and above the line.


However, to expand on point 1 above, learn to double the opponents to truly penalize them for their unsocial behaviour, and enhance your defensive skills to get those extra tricks that turn a collected penalty of 100 or 200 into 800 or even 1100. A couple of those should slow down your opponents penchant for stink bidding. 

If collecting penalties is still insufficient, offer to play for a little pocket change. A one cent a point stake over 3 or 4 hours can comfortably net $40 to $80 profit over weak players. There are two common forms of scoring in money bridge: rubber and four-deal or Chicago. Tough money players will deliberately play rubber against weak players as it creates additional strategic considerations that those players fail to grasp. Only against players that they respect do they opt for Chicago scoring, as it reduces the luck element. 

Finally, I will note that the scoring of doubled not vulnerable under-tricks was changed about 20 years ago. Formerly all doubled undertricks after the first were scored at 200 points each, but long experience revealed that this was inadequate. A change was made that the 4th and subsequent doubled undertricks not vulnerable undertricks  now became 300 points each, the same as when vulnerable. Make sure that you are using the current scoring table - and practice your doubling and card-reading skills.

Good luck!