The phrase "are increasingly joining" is correct and usable in written English.
It can be used to describe a growing trend of individuals or groups becoming part of a particular organization, movement, or activity over time.
Example: "More and more people are increasingly joining the environmental movement to advocate for sustainable practices."
Alternatives: "are progressively joining" or "are steadily joining".
Germans are increasingly joining in.
But now Japanese institutions are increasingly joining them.
Activists say frustrated civilians are increasingly joining in.
AI-powered systems are increasingly joining humans in the workforce.
Although Norwich teenagers are increasingly joining county lines operations, recruits largely remain inner-city children exported elsewhere.
Financially stronger Catholic-sponsored medical centers are increasingly joining with smaller secular hospitals, in some cases limiting access to treatments like contraception, abortion and sterilization.
Their number has been growing in recent years, and they are increasingly joined in political sympathy by Republicans and Democrats who find their parties captive to a base, fringe, or interest group with which they have little in common.
Feelings of empathy and shock are increasingly joined by worries about the consequences the refugee crisis will have on society, welfare institutions and labour markets.
Senior executives have been increasingly joining the classes and re-enacting the speech in which Henry V urges his "band of brothers" to fight to the death.
Israel announced today that seven Arabs with Israeli citizenship had been arrested for assisting a suicide bomber, further heightening apprehensions that Israeli Arabs were increasingly joining in the violent tactics of the Palestinians.
The product took advantage of two major trends at the time: the growing affluence of consumers, which was driving their desire for greater convenience, and the fact that women were increasingly joining the workforce.
