The engineering union at United was only 5-6 years old and came out of the bankruptcy when people were getting laid off and those who were kept were having to spread the work over fewer people. However the union never successfully negotiated a contract, so it was virtually worthless. I'm not surprised they voted against it. Paying dues to a union that can't even come up with a contract does not make sense. The union was a threat that engineers would not take the constant cuts when UA
was whittling down. That threat has passed for the most part.
Engineering unions are not as common and usually not as successful or strong as other unions at airlines. Pay in engineering is not really union dictated, but rather industry dictated. An engineer with 15 years experience at UA
will easily get hired by another airline or Boeing, etc and maintain the same pay and be treated as a senior engineer (except when non-revving) at whatever new company he goes to. Unions help when management forces relocations, forces uncompensated overtime, cuts healthcare etc. Seniority is not key as it is pretty meaningless except when flying standby or weeks of vacation.
If you have never designed an airplane part before, let the real designers do the work!