Why learners can't develop good English speaking skills?

[Kennen]

To develop good English speaking skills learners must have adequate regular long-term practice in listening comprehension and speaking in English. Therefore grammar learning is not to be blamed for poor speaking skills of learners. Do you disagree with that?

All authoritative reputable ESL teacher training institutions (colleges, universities), courses, publications (of Oxford University Press, Cambridge University Press, Longman ESL, etc.) and ESL schools worldwide (not just in English speaking countries) advocate active conscious and not passive intuitive ESL/EFL grammar learning.

Successful learning and mastering of a second/foreign language depends on a number of factors.
It is a good idea to analyze the factors affecting successful language learning, especially such issues as diligence, dedication, motivation/needs, interest, memory capability, methods and practice activities, content of materials, etc.

Learning, practising and mastering a new language is a long process. In addition to formal and self-study classes there should be adequate regular long-term practice in using a second/foreign language (including communication with native speakers) to accelerate success by learners.

All language aspects and skills must be learned and practised to eventually master a language: phonetics, grammar, vocabulary, listening comprehension, speaking, reading and writing.

No single course can help you master a language thoroughly, for example vocabulary and comprehensive conversational content on a multitude of topics. Only a combination of the above mentioned components can ensure mastery of a language.

Thought-through content for practice is crucial to first encompass relevant content for one's needs as there is an enormous amount of diverse content in language resources.