About 25% of adults (a little lower than that for the under 30 crowd) have genital herpes -- plus or minus. That number may be creeping up, but it hasn't been skyrocketing and over the past decade it's been pretty stable. Yes people still get it, but the numbers are not skyrocketing.
Other STDs -- especially ghonorrhea and syphillis are proportianately on the rise. The big problem with both of these is there are more drug resistant strains showing up in the general population. Sorta takes the fun out of casual sex!
There are few things that make an answer to your question less than straight forward:
1. People who have herpes do not always shed enough of the virus to transmit it. (Unlike bacterial STDs where transmission is generally automatic).
2. It is possible to transmit the virus in the absence of a noticeable OB (i.e. no symptoms). A small percentage of time when people are symptom free they are still shedding enough of the virus to possibly transmit it to a partner.
3. Not all people with herpes are aware they have it so they may engage in sexual activity when they are having a symptomatic OB (which is when people are most likely to transmit the virus).
4. Suppressive therapy to protect partners has been recognized and in use for about 10 or so years. It is helping keep the transmission statistics much lower in discordant couples (i.e. where one person has it and the other doesn't).
It's easy to avoid if you always use a condom, a behaviour that too many people avoid or give up. Condoms aren't perfect, but they do work well when used consistently.
If more doctors routinely screened for HSV1 and HSV2, that would also help lower statistics. Unfortuantely, most standard STD panels do not include blood tests for HSV1&2.
A general change in attitudes about STDs. If more people could get around the "shame" aspect of possibly having an STD and recognize it as something that simply needs to be tested and appropriately treated many STDs would not be on the rise like they currently are. Unfortunately, people avoid getting routinely screened for STDs even when they have multiple partners and/or noticeable symptoms down yonder. The biggest group at risk for contracting any STD is teenaged girls--unfortunately younger people do not believe their partners could have STDs and avoid going to doctors. They also avoid doctors to avoid their parents finding out about their sexual activity.
With the prevalance of genital HSV, if it was easier to transmit than it is, it wouldn't be long the majority of the population were to have it genitally.
Hoe eet jy 'n olifant? Bietjie vir bietjie.
(Translation from Afrikans: How do you eat an elephant? Bit by bit.)