People do convert to Sikhism, but Sikhs don't focus as heavily on getting people converted. The religion is inclusive, and is generally quite welcoming, but there's hardly any appetite for forcing it upon others. This is primarily because the religion is secular at its very core. It had a pivotal role in standing up for rights of other religions during the Mughal rule in the Indian sub-continent. And, there's also the belief that just by putting on the 'Sikh' label, you don't really gain anything. The ultimate purpose is to just become a better human being (the barometer here being the teachings of Guru Granth Sahib, which is generally quite humanistic in its approach. The authors in fact include a number of non-Sikhs). As long as you're a good human being (as in help others, meditate and earn honestly to be basic), it doesn't matter what label you are, is one of the core beliefs. Converts aren't looked down upon, because almost everyone really converted at some point in time, as it's around 500 years old as a religion. On a side note, you'll sometimes hear its 300 years old, but that's incorrect, as that event refers to the birth of Khalsa. A Sikh should generally aim to become a Khalsa. Becoming a Khalsa is kind of similar to baptism, but it's voluntary and mostly done when you grow up and feel you're ready for it (some teens do it under the influence of parents, but I, along with many other Sikhs probably, tend to believe that is against the spirit of the religion. People in early teens don't have a full understanding of what they want, and that's why parents shouldn't do it for them IMHO). I'm in my late 20s and not a Khalsa, for example. And, there are many (probably the majority) like me, not Khalsa but just Sikh.

An example is - I studied in two different schools. The first school was Catholic, and I studied there for 12 years. The management used to heavily encourage conversion. For students, there were some benefits like no tuition fees, and maybe some other stuff. For teachers, it was probably a better career. I spent another 2 years in a Sikh school. In that school, rewards were totally independent of religion. If you scored above 90%, you'll get your tuition fees waived. If you were a single girl child (due to female infanticide in the region), I think they did something as well. There was no focus on converting non-Sikhs. This is not to diss on Catholicism, as I've respect for Christians in general and I personally know many good ones, it's probably just that my school didn't do it right. I just find being charitable only to people who are the same religion as yours, not a great idea. Religion shouldn't be a consideration during charity (and in conduct towards people otherwise too).

(edited for clarity)