For the same reason that there were no female attendants as part of worship arrangements *in* Jehovah's Temple serving along with the Priests. They were only allowed to serve outside the Tabernacle perhaps drawing water and washing the priestly garments (Ex.38:8).
Are you complaining about Jehovah's arrangements?!!
Witnesses follow the pattern set by Jehovah God Himself regarding the arrangements for worship. And we follow Christ and the Apostles pattern in the Christian congregation. Even when appointments were made for taking care of the material needs of those in the congregation it was qualified men, not women (Acts 6 :2-6).
On the other hand, women can preach and teach outside the congregation. In fact, in most areas women are the ones who are most active in the preaching work (Ps.68:11; Isa.40:9; Ac 2:17-18). Women along with the men received the holy spirit and joined in declaring "the magnificent things of God" (Joel 2:28, 29; Acts 1:14; 2:1-11). Christ gave the Great Commission to preach to all his disciples, men and women (Mt.28:19,20). Women could also teach other women and children in the congregation (Tit.2:3,4; 2Tim. 1:5; 3:14,?15).
However, even though women equally received the gifts of holy spirit, including "prophesying" or preaching God's words, their use of this gift was regulated by the God given principle of headship (1Cor. 11:3-10). Paul goes on to say that this arrangement for order in the congregation is from God and not from man (1Cor. 11:11,12), and therefore he concluded that there was no room for dispute on this question (1Cor. 11:16).
True Christians today feel the same way. We are not the ones who make the rules regarding who is to teach within the congregation. Jehovah has set out the theocratic order for men and women. As the creator Jehovah knows women much better than any man does and he knows how women can best serve him to his praise.
The theocratic order set out by God is that women (even those of the 144,000) were not to teach, or exercise authority in the congregation (1Cor. 14:34,35; 1Tim. 2:12).
This does not mean that a woman can never speak in a meeting of the congregation. Women as well as the men received the gifts of the spirit, including those of speaking in tongues and prophesying, and these would require them to speak in the congregation. At congregation meetings dedicated women may participate by giving comments and sharing their experience during study sessions and thus build up all in attendance. However, women were never to exercise authority over the men as a teacher or instructor of the congregation.
To put this in proper perspective we must also note that there are also anointed men of the 144,000 who do not have equal privileges of oversight or teaching within the congregation(1Cor. 14:34,35; 1Tim. 2:12; 3:1-7; Tit. 1:6-9; Js. 3:1).
Jesus himself indicated that not all his followers would have the same responsibilities (Mt.25:14,15; Mk.13:34; cf. 1Pt. 4:10). The phrases "each one according to his own ability" and "to each one his work" indicates that not all Christians had equal abilities nor assignments.
So while certain congregation privileges were not open to all Christians they did not feel any incongruity in this arrangement. Because both men and women in the True Christian congregation know the Scriptures and abide by the arrangements that God Himself instituted. And all still contributed to providing spiritual food in whatever capacity God assigned them.
Women were still given great privileges and responsibilities within the congregation. Women were the first to witness his resurrection and were to convey this information to the Apostles and other men (Mt.28:1-10; Jn 20:11-18). Women played an important, though not dominant, role in the spread of Christianity (Ac. 12:1-5, 12). Women were privileged to be Christian prophetesses (Acts 21:9; 1Cor.12:4,?10).
Jehovah created the woman as a complement of the man (Gen. 2:18). Hence, the wife's position in relation to men in no way implies inferiority. It is patently clear from the Scriptures that "there is no partiality with God" with regard to race or sex (Rom.2:10,?11; Gal.3:28).
Modest, God-fearing men and women do not ambitiously promote themselves, as Satan and those who imitate him do.
We can be thankful that resurrected faithful women share in the Kingdom as rulers. While those in heaven are no longer male or female those who lived as women retain their intimate understanding of the feelings and experiences of women! (A strong caution to some men and their attitude!)