Some women have difficulty attaining orgasm... especially those who avoid masturbation... or those who masturbate often with a vibrator.
A person can become accustomed to a specific type of stimulation that a talented tongue simply can not match.
With a woman who has avoided sexual release, patience, perseverance and developing her trust in you will eventually solve it. ( eta and by 'eventually" I mean give it six months of concerted effort)
With a woman who uses a vibrator, just getting her to knock of the vibrator for a while will allow her to regain response to a different stimulation.
With a woman who knows her own body, and can offer constructive, on the job feedback... then pleasing a woman is something even an inexperienced man can do just fine... as long as he is willing...
However... Lots of guys do suck at sex, in general, and dislike giving oral sex in specific.
It does require a willingness to brave a charleyhorse in your tongue, and yet keep going.
My most favorite thing about giving a woman head is the multiple orgasm thing.
Not just the orgasm after orgasm thing... but the crescendo...
Consistent and persistent stimulation can bring a woman to many orgasms in a row... each successive orgasm coming on faster and with shorter intervals between... until she is in a delirium of orgasmic ecstasy... like one long unending orgasm.
Once in this state... just about ANY rhythmic stimulation will cause climax.
You can switch to intercourse and find she will orgasm just from the pounding sensation...over and over...
Or, as I discovered with one kinky woman in particular, spanking will bring on orgasm.
Unfortunately, not all women can tolerate this kind of intense and unrelenting stimulation... many prefer a "refractory" period of lesser or no stimulation between orgasms....
Even with these women... if you are willing to run your tongue on idle for a few minutes, you can give them 15 or 20 orgasms in single sitting.
But the key is to be sensitive to her response, to find her "frequency" and her ideal stimulation zone ( not always directly on the clitoris ) And be persistent.
And be sure to keep your arms out of the way as the padded safety rails clamp down on either side of your head...