PostgreSQL 10: deleting foreign key locks selects
Foreign key constraints are implemented as system triggers in PostgreSQL.
This query shows you the triggers behind your foreign key constraint:
SELECT t.tgrelid::regclass AS table_name,
       t.tgname AS trigger_name,
       concat(
          CASE t.tgtype &amp; 66 WHEN 2 THEN 'BEFORE ' WHEN 64 THEN 'INSTEAD OF ' ELSE 'AFTER ' END,
          CASE WHEN t.tgtype &amp; 4 &gt; 0 THEN 'INSERT' END,
          CASE WHEN t.tgtype &amp; 8 &gt; 0 THEN 'DELETE' END,
          CASE WHEN t.tgtype &amp; 16 &gt; 0 THEN 'UPDATE' END
       ) AS fires,
       f.proname AS trigger_function
FROM pg_trigger AS t
   JOIN pg_proc AS f ON t.tgfoid = f.oid
   JOIN pg_constraint AS c ON t.tgconstraint = c.oid
WHERE c.conname = 'incoming_account_id_fkey';

 table_name |         trigger_name         |     fires     |   trigger_function   
------------+------------------------------+---------------+----------------------
 account    | RI_ConstraintTrigger_a_62074 | AFTER DELETE  | RI_FKey_noaction_del
 account    | RI_ConstraintTrigger_a_62075 | AFTER UPDATE  | RI_FKey_noaction_upd
 incoming   | RI_ConstraintTrigger_c_62076 | AFTER INSERT  | RI_FKey_check_ins
 incoming   | RI_ConstraintTrigger_c_62077 | AFTER UPDATE  | RI_FKey_check_upd
(4 rows)

You see that two of these triggers are defined on the target table, account.
If you drop table incoming, that will also drop the foreign key constraint and consequently drop the triggers on account, which requires a short ACCESS EXCLUSIVE lock on account.
That should not be disruptive, but it seems that you are running long transactions that involve account. Now the DROP TRIGGER on account has to queue behind the currently active transactions that hold locks on account, and all later transactions have to queue behind the DROP TRIGGER, which is what you observe.
You will have to find a time when there are no long running transactions involving account, then your DROP TABLE will finish quickly without blocking other sessions.
Side remark: choose bigint rather than integer for artificial primary key columns.