As i read text from canon. It seem like in the budda day jhana was a lot easier and highly recommended for the fold path. But now it seem like this rare thing only a handful of people can attain. If it was so easy how can we find the path to enter it without all the complication?
One thing has to be understood that people who joined the Buddha many of them were already trying on different ways to attain liberation. Like Mahakasapa and Sariputta were already asectics practising elsewhere. And that time in India was really a peak for people trying attain Nirvana. So many people must have been ready psychologically to attain jhnana. They just needed right instructions.
Even for today you need right teacher to get there and a firm practise. I have heard in some youtube talk by Ajahn Brahm that a retreat participant with him attained jhnana. I am just not able to find that video atm.
Besides, so many Buddhist monks meditating everywhere must be achieving jhnana they just have no need or even bother about putting it on internet and tell everybody about it. They might not even have the resources.
Besides, its very important for advancing on the path that your spiritual experiences should be kept secret and should only be discussed with your teacher. This rule is like 101 of practising spiritual path.
That leaves us with rest of us internet noobs who have recourse to internet and can discuss such things and who dont attain it.
So the point is, you just dont hear it. The difficulty level is left unchanged by the system.
All my teachers without exception said that the idea of "goal" that you are striving to "attain" is THE final obstacle to attainment.
To that aim, one is advised to completely eradicate the idea of goal from one's mind. As in, on the deepest emotional level you have to give up any slightest hope, dream, or intent to attain jhana - and keep meditating on the resulting state.
There is probably lots of propaganda in the Pali suttas. For example, if the core of the Pali suttas are actually understood then the doctrinal perversions in Buddhism that arose less than a few hundreds years after the Buddha's passing (including doggy suttas placed into the suttas) give the impression there could not have been as many arahants as the suttas claim.
Also, at least in the West, many people with jhanic potential are Christians.
As for reaching jhana, it is not complicated. SN 48.10 refers merely to "letting go of craving" as the way to reach jhana (which includes letting go of craving for jhana).
It has not become harder. These things have always been hard.
Even to be born as human and getting the chance to listen to the Dhamma is also rare and hard.
From Dhammapada 182:
Rare it is to gain birth as a human being.
Difficult is the life of mortals.
Hard is the hearing of the Sublime Truth (Dhamma).
Rare is the appearance of the enlightened ones.
Kiccho manussa patilābho
kiccham maccāna jivitam
Kiccham saddhamma savanam
kiccho buddhānam uppādo
I guess it was equally equally achievable. Hard or Easy is only relative. From my personal opinion, the reason for less and less to achieve jhana or even Arahant-hood, is because the effectiveness of teachings of the dharma is gradually less as 'original' as time passes.
Entering jhana, or dhyana is facilitated by merit and virtue. The elders had ALOT more merit and virtue (they had accrued much more blessings, generally speaking). That's why they only needed to hear the Buddha say a couple of phrases to get enlightened.
Personally, I strive for cultivating blessings and morality as the foundation for entering dhyana. It's hard.