The recent Continuous decrease in POB token price, do you think is any related to the having difficulty in accessing the tribe via proof of brain front ends.

No, I don't think so. Sellers Sell POB through Hive Engine, Tribaldex or Leodex. Until they have access to it they will keep selling.
Harsh Reality is There had always been and there will always be People who will keep selling their Tokens no matter the Price. Because for them it's just a Token or Easy to get Money method.

what do you think can be done to have an increase POB token price?

First of all we need to maintain a Standard of POB, some users take POB for granted because of good rewarding service of the community. That should not be the case, I fear of this goes on we might end up like other Tokens BHT, Lern, Neoxian etc.
We need to create scarcity of POB and that could be done via Burning and Staking.
An advice to all panic POB sellers, Staking is the best option on POB, it's the best investment but If you don't want to stake its your choice but please make a vow to yourself to don't sell POB much cheaper, try to hold your liquid POB and wait for Price Push unless it's very critical. Meanwhile try Delegation method, You can delegate your POBs to Top curators like @scholaris.pob, @onealfa.pob or if you want to profit from delegation too then delegate your POB to @brofi and receive rewards in BRO coins. Make a threshold limit price for yourself and stick to it no matter what i would not sell below this price, that will definitely help in giving stability to POB Price.