Why would that be necessary? Are they members of the UN? That is not what you mean is it? They probably want to do things their own way instead of abide by the rules of the security council. The US is in the UN and it's a terrible deal for us. We have to pay huge dues every year and get no real benefit from it. In fact, they are making lots of things worse.
because the security council generally frowns upon the ideas of those countries so instead of being put in a position of having to challenge their reasoning for not participating within the counsel they choose not to be permanent. they would be giving up much of their freedom to pursue the advances in their own securities as far as military technology, and much of their secrets could be possibly exposed or even persuasively put to a stop. and these countries don't want to waste time, money or effort. they are mainly focused on their country's gains and not trying to police the world. our country's government could learn from them. of course we have to be involved with other countries because financially and economically we need them. the majority of the tax payers money is over seas.
As Vicky says, it has to do with the heritage of WW2. After the war, West Germany was kind of "on probation" and East Germany was a communist country. Only since the reunification the attitude of the security council member countries has slowly changed. However, Germany is also known for standing to its own opinion and has refused to share the US position on some occasion in recent years. That is perhaps one reason why its not a permanent member yet. About Japan, I don't know enough details to tell.
There have been several proposals to add new permanent members, along the lines of the G4. The nations usually mentioned are Brazil, Germany, India, and Japan. They mutually support one another's bids for permanent seats. Britain, France and Russia support G4 membership in the UN Security Council. This sort of reform has traditionally been opposed by the "Uniting for Consensus" group, which is composed primarily of nations who are regional rivals and economic competitors of the G4. The group is led by Italy and Spain (opposing Germany), Mexico, Colombia, and Argentina (opposing Brazil), Pakistan (opposing India), and South Korea (opposing Japan), in addition to Turkey, Indonesia and others. Since 1992, Italy and other members of the group have instead proposed semi-permanent seats or the expansion of the number of temporary seats. So your suggestion that several countries should be added to the security council has been discussed, but it is not without controversy.